Hi Jamie and Eric,
This is actually controlled by a setting in the theme.skin file. If you look for this in your theme.skin file:
<asp:CheckBoxList runat="server"
CssClass="aspcheckboxlist"
RepeatColumns="2"
RepeatDirection="horizontal"
RepeatLayout="Table"
/>
you could change it to 1, but that may (and maybe not) also affect other checkbox lists in the site. If it causes a change elsewhere that you don't like you could work around it by copying your skin with a new name, change it only in that skin and then set that as the skin for the Form Wizard page.
What I will do for the next release of Form Wizard is add a SkinID to the checkbox list so that then you could use this:
<asp:CheckBoxList runat="server" SkinID="FormWizard"
CssClass="aspcheckboxlist"
RepeatColumns="1"
RepeatDirection="horizontal"
RepeatLayout="Table"
/>
which would only affect the Form Wizard checkboxlists
Best,
Joe