are you sure your style is "in-text"?
I.e. have you double checked that you have
<style xmlns="http://purl.org/net/xbiblio/csl" class="in-text" xml:lang="en">
at the top of they style?

What you describe sounds odd, frankly: There is no reason Zotero would superscript the citation number. There is also no reason it should leave out the locator for the citation section you have - which looks good (although you probably don't want both p. in the prefix and "label variable" - this will give you p. p 32 instead of p. 32).
Have you tried this in the test pane? How does it look there?

Cool, please make the style available once you're done.
Here is the Zotero test pane:
chrome://zotero/content/tools/csledit.xul
it's absolutely indispensable for modifying styles, I admire you for having made it so far without it.

Whether initiated by my comment above or by coincidence i just received authorization to access SVN/Trac . (Thank you.) However, I can't find how to submit a style. I'm going to provide it here. This meets the requirements for the BMJ Group journal Injury Prevention.

I'm going to provide it here.

<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="http://xbiblio.svn.sourceforge.net/viewvc/*checkout*/xbiblio/csl/schema/trunk/csl.rnc" type="compact"?>
<style xmlns="http://purl.org/net/xbiblio/csl" class="in-text" xml:lang="en">
<info>
<title>Injury Prevention</title>
<id>http://www.zotero.org/styles/injuryprevention</id>;
<link href="http://www.zotero.org/styles/injuryprevention"/>
<author>
<name>Julian Onions</name>
<email>julian.onions@gmail.com</email>
</author>
<author>
<name>Michael Berkowitz</name>
<email>mberkowi@gmu.edu</email>
</author>
<contributor>
<name>David Lawrence</name>
<email>david.lawrence@sdsu.edu</email>
</contributor>
<category term="numeric"/>
<category term="medicine"/>
<category term="public_health"/>
<category term="sociology"/>
<updated/>
<summary>The Injury Prevention (a BMJ Group journal) style is a modified and hybrid version of Vancouver and AMA styles: In-text citation =square brackets, collapsed. Bibliography- doi strings always when available; special punctuation and spacing; first author and journal volume bold; journal abbreviation italics; authors et. al four or more; year-only date; page numbers for quotations via add/edit citation dialog b ox.</summary>
<link href="http://injuryprevention.bmj.com/site/about/guidelines.xhtml"/>
</info>
<macro name="editor">
<names variable="editor">
<name name-as-sort-order="all" sort-separator=" " initialize-with="" delimiter=", " delimiter-precedes-last="always"/>
<label form="short" prefix=", " text-case="lowercase" suffix="."/>
</names>
</macro>
<macro name="anon">
<text term="anonymous" form="short" text-case="capitalize-first"/>
</macro>
<macro name="author">
<group suffix=".">
<names variable="author">
<name name-as-sort-order="all" sort-separator=" " initialize-with=""
delimiter=", " delimiter-precedes-last="always"/>
<label form="short" prefix=" " suffix="" text-case="lowercase"/>
<substitute>
<names variable="editor"/>
<text macro="anon"/>
</substitute>
</names>
</group>
</macro>
<macro name="author-short">
<names variable="author">
<name form="short" and="symbol" delimiter=", " initialize-with="."/>
<substitute>
<names variable="editor"/>
<names variable="translator"/>
<text macro="anon"/>
</substitute>
</names>
</macro>
<macro name="access">
<group>
<text value="Available at:" suffix=" "/>
<text variable="URL"/>
<group prefix=" (" suffix=")">
<text term="accessed" text-case="lower" suffix=" "/>
<date variable="accessed">
<date-part name="month" suffix=" "/>
<date-part name="day" suffix=", "/>
<date-part name="year"/>
</date>
</group>
</group>
</macro>
<macro name="title">
<choose>
<if type="book">
<text variable="title" font-style="italic"/>
</if>
<else>
<text variable="title"/>
</else>
</choose>
</macro>
<macro name="publisher">
<group delimiter=": ">
<text variable="publisher-place"/>
<text variable="publisher"/>
</group>
</macro>
<macro name="year-date">
<group prefix=" ">
<choose>
<if variable="issued">
<date variable="issued">
<date-part name="year"/>
</date>
</if>
<else>
<text term="no date"/>
</else>
</choose>
</group>
</macro>
<macro name="edition">
<choose>
<if is-numeric="edition">
<group delimiter=" ">
<number variable="edition" form="ordinal"/>
<text term="edition" form="short" suffix="."/>
</group>
</if>
<else>
<text variable="edition" suffix="."/>
</else>
</choose>
</macro>
<citation>
<option name="collapse" value="citation-number"/>
<sort>
<key variable="citation-number"/>
</sort>
<layout prefix="[" suffix="]" delimiter="," vertical-align="baseline">
<text variable="citation-number" />
<group prefix=", ">
<label variable="locator" form="short" include-period="true" />
<text variable="locator"/>
</group>
</layout>
</citation>
<bibliography>
<option name="line-spacing" value="2"/>
<option name="hanging-indent" value="false"/>
<option name="et-al-min" value="4"/>
<option name="et-al-use-first" value="3"/>
<layout>
<text variable="citation-number" prefix="" suffix=". "/>
<text macro="author" suffix=""/>
<choose>
<if type="book">
<group suffix=".">
<text macro="title" prefix=" " suffix="."/>
<text macro="edition" prefix=" " />
<text macro="editor" prefix=" (" suffix=")"/>
</group>
<text prefix=" " suffix="" macro="publisher"/>
<group suffix="." prefix="; ">
<date variable="issued">
<date-part name="year"/>
</date>
<text variable="page" prefix=":"/>
</group>
</if>
<else-if type="chapter">
<text macro="title" prefix=" " suffix="."/>
<group class="container" prefix=" ">
<text term="in" text-case="capitalize-first" suffix=": "/>
<text macro="editor"/>
<text variable="container-title" font-style="italic" prefix=" " suffix="."/>
<text variable="volume" prefix="Vol " suffix="."/>
<text macro="edition" prefix=" "/>
<text variable="collection-title" prefix=" " suffix="."/>
<group suffix=".">
<text macro="publisher" prefix=" "/>
<group suffix="." prefix=" ">
<date variable="issued">
<date-part name="year"/>
</date>
<text variable="page" prefix=":"/>
</group>
</group>
</group>
</else-if>
<else>
<group suffix=".">
<text macro="title" prefix=" " />
<text macro="editor" prefix=" "/>
</group>
<group class="container" prefix=" " suffix=".">
<text variable="container-title" font-style="italic" form="short" suffix=""/>
<group delimiter=";" prefix=" ">
<date variable="issued">
<date-part name="year"/>
</date>
<group>
<text variable="volume" font-weight="bold"/>
<text variable="issue" prefix="(" suffix=")"/>
</group>
</group>
<text variable="page" prefix=":"/>
<text variable="DOI" prefix=". doi:"/>
</group>
</else>
</choose>
<text prefix=" " macro="access" suffix="."/>
</layout>
</bibliography>
</style>

Thanks for contributing this!.

Before I or someone else submits this - would you consider adding the CC license?
<rights>This work is licensed under a Creative Commons Attribution-Share Alike 3.0 License: http://creativecommons.org/licenses/by-sa/3.0/</rights>;
right above </info>

and the link to the style guide should have rel="documentation" after it
<link href="http://injuryprevention.bmj.com/site/about/guidelines.xhtml" rel="documentation"/>

thanks - it's committed and will show up on the repository soon.
If you'll contribute more styles it will be worthwhile familiarizing yourself with validation - there were a couple of small glitches (that I fixed):

- text-case has to be "lowercase" - just 'lower' doesn't work
- the <rights> have to be above, not below </info>
- their is no public_health category in the csl schema.
Otherwise looks great and thanks again for contributing.