I only have a front cover and a back cover. Can I upload one blank page and note that all the inside pages should follow this same format?

In that case, you can only upload the file for the cover. When you select your product options and get to the file upload section, you can turn off the 'Multiple files' button. This will allow you to upload only one file without getting the error message.

To let us know the inside pages are blank, you can leave a comment.