I also was going to suggest you use a walking foot with straight line quilting. When I free motion, I pin baste and then I start quilting in the center. When I have a portion of it done, I will lay out the quilt and redo the pins and straighten the fabric once again. It is an extra step but seems to work for me. Stay positive and don't give up. Eventually it will work better for you. I learned much along my quilting journey.