It appears you are stopping too often. Visualize the entire loop and do it in one sweep of the hand. You might also be trying to keep the fabric moving. When you feel you are loosing control of the fabric because you need to move the hands. That is the time to stop and reposition. Also when you start up again let the needle move in place for a stitch or two until you have firm grip and then move out. It has been my experience that FMQ ers try to keep the fabric moving. Which causes irregular lines.