I see now. Are you planning to add just to the sides? If the pic is the quilt on top of a queen size bed, you probably want bigger borders then the 4 3/4" I came up with. You could probably add 10" to each side, depending how much drape you want. But solid 10 1/4" blocks seems like it might be too much (how big are the star blocks?). You could do 2 rows of 5 1/8" blocks (cut at 5 5/8") on each side if you wanted smaller blocks (basically, make each 10 1/4" block a 4-patch). Unfortunately, I can't get any other multiple to work out evenly.
Good luck. The quilt is lovely so far. I like the way you used both panels.