Thanks for your responses. I put together 20 (five rows of four) rectangles so the towel would be a rectangle. Seams were a narrow zigzag with a short stitch and alternated so there would be raw edges on both sides of towel. On the ends I used the cuff hems from the shirt. (It was a short sleeve shirt.) On the long edges I made exposed seams, that is, folded over only once. It's been through the washing machine once and there are a lot of loose threads. Once those are trimmed, I think it should be pretty stable.