Thank you all for your help! I wound up sewing a tiny piece on the backing to try to make up the difference. It is noticeable on back, but not too bad.
Then I sewed binding to front and hand-sewed to back. I didn't want to lose my star points, and after all the problems, I didn't trust myself to machine bind it.
Not really happy with the binding...probably should have went with the star-colored fabric like I was thinking, but I thought I wanted a more muted binding. All in all, I would have done a bunch of things different, but it's done except for clipping threads and trying to work out some of the puckers.
I definitely need more practice....