As others have said, being a little wider or the back isn't a problem unless it bothers you. You could also make the binding wider by still sewing it the quarter inch on the back but adding more batting to 'stuff' the binding. Just cut narrow strips of batting and stuff as you go. If you do decide to remove the binding to cut it down, I would suggest cutting a new binding if you have the extra fabric. No matter how careful you are removing it, it will stretch and you might have a problem resewing it so it stays nice and flat.