Uploading an album with a single first/last page is a different process than uploading an album with spreads only. This article will take you step by step through that process.
Start by uploading your revision as usual. When you get to the Edit Revision step, make sure to select Add Cover if you don't have one on your album.
Move your front cover to the proper place by clicking on the front cover and dragging it to the beginning of the album.
You will receive a pop up warning that your first page needs to be resized. Click OK.
The software will resize those pages for you, adding a blank page to the left and right of your single pages. Click Next.