I have added a border to make it large enough, trimmed them down to fit, used them in the backing and thrown them away (only one from a block lotto at my LQS). Last year when I made 12 quilts for soldiers using donated blocks from all over, some folk's didn't know what a 12.5" block was, but I used every single donated block in the quilts - sometimes the front and sometimes the back. Those quilts turned out awesome!!! I like having extra blocks and material from the front incorporated into the backing...makes the backing more interesting!