HI G, Sorry you are having so much trouble. Round edges do stretch so treat them with care. First finish everything but the top and then try the following. One idea to try is a hand gathering stitch at the center. You can then lay it flat and gently pull it in a little bit until it lays flat. Be sure to spread the gathers out around the whole circle. Then first baste the binding by hand, check it, then sew again by machine. You may pm me also for help. Do you have a picture you could email? I really hope this helps.