I think this has happened to all of us :wink: It was good you ordered extra backing and a good thing for all of us to remember to do :D:D:D
Also, sometimes you may get a great inspiration to add an additional row or border, and you then you will still have enough... any extra backing fabric can always be used to make a pillow or another accessory to match your quilt :wink: A quilt as a gift and then accessories for a future gift :D:D:D