Free-motion quilting is so different when you are quilting a big quilt rather than a practice sandwich. Mastering the relative speed of your hands and foot control is much harder when you have the weight of a larger quilt dragging and pulling on the needle. It can be very fatiguing, too. Be sure to give yourself breaks where you get up and walk around and try to relax your neck muscles. Try to think of just the area you are working on, not the whole thing. I usually start in the middle, which is the most difficult area, since it has the most loose fabric all around. If the quilt is big enough, try throwing some of it over your shoulder to support it. And don't do it when you are tired. You'll feel frustrated and discouraged. Just keep at it and it will become better. Good luck!