I have seen this done on a quilt. They usually leave a one inch wide strip. Do miter corners. And yes, I have seen a decorative stitch used. Before folding backing over, clip off the points on each corner almost even with the front of the topper as this makes the mitering easier using the backing over front method. Fold the backing over with raw edge meeting edge of topper; fold over again making the double fold, then stitch down.