Personally, I would add a piece of bating to it. However, I made a quilt that was already binded larger by adding another border. The last border has no batting in it, and the results were satisfactory. It was a quilt that had shrunk, and I would do it again if I had to. It looks okay. But, I would be happier with a new quilt that had batting in all of it.
Not much help, huh?
Dina