I agree with those who've suggested bias binding since you've already quilted it. It's really not that difficult with a walking foot & some clips (Wonder Clips, those silver barrette-like things, or even clothes pins, binder clips or large paper clips can work). If you run into trouble, you can snip the unfinished edge of the binding up to the seam (leaving 1-2 threads between the top of the cut & the seam) if the quilt is bunching or can cut out a small triangle shaped piece using the same technique if the binding itself if bunching. Just measure around the outer edge of the quilt and add 10-12" like usual -- the bonus is that you don't have to miter any corners!