I agree that the batting issue is probably that it wasn't loaded on the frame square, or it developed a pleat as you advanced it. The batting should be cut several inches larger than the quilt top just for this reason. If easing it over as you advance the quilt doesn't help, you can add a wedge at the end. Remove the bottom portion of the quilt from the frame, butt the new piece of batting against the original one and whip stitch. Another thing is as you advance the quilt, smooth it by hand and run a row of basting stitches down the sides before you start quilting the center. If the ends are really loose & floppy, it may be the backing isn't square or you are putting a much denser quilting design in the center.