So your quilt is already sandwiched?? Maybe you should REALLY take it apart and resandwich. Lay the backing on a hard flat surface, smooth and tape the corners. Then take a tape mearsure and measure the diagonal lenghts. They should be the same. If they are not, stretch and re-tape the backing. Then put on the batting and then put on the top and measure the diagonals again and adjust. THEN PIN PIN PIN!! I try to pin every 4 inches. If you do that, as long as you are not using a super loft batting, you should not get any folds.