I bring the back around and fold it over. I cut it about one inch larger than the top and then fold it in half, then in half again. It helps if you press it. Then I use a zig-zag or blanket stitch. It turns out great. Sooooo easy. I don't use any pins, except maybe at the corner where I just fold one side over the other and stitch the mitered seam to hold it closed.