I'm not quite sure whether you mean that your stitches are uneven, or that the design itself isn't as smooth as you would like. Other causes of jerky design could be that your machine hangs up on something, even slightly (check the cords/cables to be sure they aren't catching on anything); the machine bumps into something, such as the rolled up quilt top or rail; or the wheels are running into something (such as thread, lint, uneven spot in tracks). I also have problems if I try to continue quilting to my right (or left) too far. I do better when I'm more in front of the machine, but sometimes I try to keep going without moving my feet.