you very well might have some curling, but nothing some good blocking shouldn't take care of. Since the item will be wet when it is done felting, you have an opportunity to do all kinds of shaping as it dries and you can continue to shape it as it's drying. That should take care of it or if you're really worried, you can try adding an I-cord edge to minimize the rolling a bit. Blocking and shaping should suffice, though. Good luck!