Spacious theme with iTheme Exchange shopping cart

My iTheme Exchange shopping cart is supposed to be running through either the archive.php or category.php page, and they provide a tutorial on how to get rid of the sidebar on those pages. However, when I edit the archive.php page, nothing changes, and in Spacious, there is no category.php page. So it’s not clear to me where the URL mysite.com/category/ is being generated so that I can try to remove the sidebar?
The reason I want to do this is because it doesn’t make any sense to have my blog sidebar on the same page as my shopping cart. iTheme’s support doesn’t cover a situation where there is no category.php page.
Any advice would be greatly appreciated.