Instead of tying the two layers together, you can also use very small zigzag stitches (set stitch length at 1 or a little less, let needle going in 6 or 8 times at each spot) and space them 6 or 8 inches apart evenly. I've done this on a couple lap quilts that had flannel on the back and no batting, works very well to hold the layers together. I did bind them instead of sewing around the edges, and I pulled the threads up, tied and buried for a little extra security in each stitch.