Next, moisten the adhesive on a second envelope. Insert this flap into the envelope that has the flap folded back (your middle page). You will want to add more adhesive later to make your album more stable. This album will be your cover/first page.
Close your book. Turn it so that the middle page flap is facing you. Moisten the adhesive on the last envelope and insert it into the pocket between the pages at the spine of the book. This will be your last page.
As I mentioned earlier, I cut down the envelope pockets slightly to make my carousel note pages easier to take in and out. I reinforced these spots on both sides to keep the book stable. I also added adhesive to the flaps where needed to make everything sturdy.
Edited to add: The completed album pictured above includes a fourth envelope for even more pages. To add another two scrapbook pages to your book (like the one I did originally) add the following steps:
Fold back the flap on a fourth envelope, but do NOT moisten the adhesive. Instead, insert the fourth envelope into the flap that is exposed in your album and reinforce with adhesive. Your flap will still be between the last two pages of your album, but you will have additional room for scrapbook pages.