Oh, Patti, of course your elastic will work fine. I sewed mine together, because I couldn't see that just glueing them would hold in the long term. As for the pockets, you probably did more than needed. Yes, I put a casing for the elastic along the top, and that was it - no sewing down the sides or bottom, as the sides get glued down, and the bottom I put a few stitches in just to hold the pleats or gathers in place, but the edges were still raw. Don't forget that all the raw edges will be hidden when these box linings get stuck to the outsides.
As for the other little problem, don't worry, we are all human, and if you make another box, you won't do that again, will you. I am dying to see the finished box, and the fabric you chose. Just people's choice of fabric makes them look incredibly different. Some do really startling interiors, just for the hell of it. I once saw one that had a bright green frog appliqued to the lining in the bottom, for a joke.