Don't cut the corners to square it up! It's not so out of square. Measure across the middle of the top in both directions. These are your measurements for binding, not the outer edges. Say top to bottom is 59¼ inches, but your edges are 60 and 59½ (forget about these measurements). Add 2 inches to the binding length for a 1 inch extension at both ends. Fold the binding in half and then in half again, and mark with pins or chalk to get the length divided evenly into quarters. Do the same for the top and bottom edges of the quilt. Pin the binding on to your quilt "sandwich." There will probably be excess "sandwich" lengths between the border quarters. Pin this excess in as best you can. When you sew the binding on, have the binding on top and the quilt on the bottom with the backing touching the presser plate of the machine. This helps the bottom layer be worked in. Stitch the binding on. I've used this method for all my quilts and it even works for sewing on binding by hand. Just work/ease any excess quilt sandwich into the binding. Repeat this for both sides. The quilt will be square and lay flat.
SandyQuilter