Use coordinating fabrics
Just cut off the binding and add coordinating borders to the size you want using a quilt as you go method. Then bind using the coordinating fabric. Not so hard.
Or - after cutting off the binding - sew on the extra borders similar to a reverse facing. Machine sew to the back, add batting, face with the front coordinating fabric, hand sew on the front and then quilt. Again not difficult.
Well, I was going to show you one I enlarged for my DGD. She didn't want to give up her baby comforter... still has it even though she's nearly a teen! Here's hoping she doesn't want it made larger again!