Start with square corners as stated. When you are sewing on your binding stop exactly 1/4" or whatever seam allowance you are using from the edge. Don't guess! Mark where to stop and back stitch. When you take the fabric from under the machine and prepare to go down the next side you need to make a perfect right triangle with your binding fabric on the bottom. Then as you bring the top layer down the folded edges need to match exactly and the cut edge should line up with outside edge of quilt. It can help to lower your feed dogs as you maneuver this sandwich back under the machine. I only do hand finished binding so can't help if you are doing machine finished.