Custom Report - show chart of number of contacts created per day

I'm trying to create a chart of the number of contacts created per day over the last 30 days and for a certain user. This is for a custom report in CRMOnline

Here is my fetchXML:

<fetch version="1.0" output-format="xml-platform" mapping="logical" distinct="false" aggregate='true'><entity name="contact"><attribute name="createdon" groupby="true" dategrouping="day" alias="day" /><attribute name="contactid" alias="count" aggregate="count" /><filter type="and"><condition attribute="statecode" operator="eq" value="0" /><condition attribute="ownerid" operator="eq" value="@user" /><condition attribute="createdon" operator="last-x-days" value="@create" /></filter></entity></fetch>

Assuming this is correct, I'm not understanding how to create my chart correctly.

Here is a screen shot of my chart in design mode

which gives me the following chart in preview:

I know that there is a total of 560 contacts created in the last 30 days by this user, most of which were imported in a single go (464) yesterday, so there should be a large spike. Can anyone see from here where I'm not understanding this?

Cheers,

Chris