I rounded the corners and did scalloped top and bottom of a quilt recently. I cheated and did straight of grain on the straight sides and bias on the ends. My quilt wasn't very wide so I just used a square of fabric and drew a line from one corner to the other on the 45º. I then used my ruler and drew a line over at 2 1/2 inches from the last line. I did the same on the other side and cut along the lines with scissors. I think I kept going until I had 3, 2 1/2 bias strips for each end. I sewed the straight binding on one side and joined on a 45º the bias strip a couple of inches before starting the corner and scallops. It worked out very nicely.