I try and have my backing 4" larger than the top, because the quilting will take up a bit of the extra. After the quilting is done I square up the top and batting (don't trim the backing yet).Sew 1/2" all around the sandwich edge, all layers. Then trim the backing to be 2" beyond the edges. Now fold and iron your binding 1/2" all around. Fold forward again so that the ironed edge meets the basting line. You can hand sew or machine sew down your binding. The corners can be mitered or straight folded. Clear as mud, right?!