If you are using a CafePress template for your Premium Shop layout, you do not need to check the Show Sidebar option. The sidebar is already in built into the template, and will result in a double sidebar. If you are not using a template, you will want to make sure the Show Sidebar option is selected in the Custom HTML are of your account.
If you are having trouble viewing your Shopkeeper Bio, please see the related FAQ: Where is my Shopkeeper Bio?