I bought a Brother cs6000. I use the darning foot--the manual refers to it as the free motion quilting foot. I set the speed control to 1/2 it's fastest setting. I also drop the feed dogs. (I have a really old Brother that came with a darning foot to cover up the feed dogs).
I always use a new needle and try to sew fast. For me, I can make better curves. I'm guessing the foot may make a huge difference for you.
If your machine did not come with the foot, you can order them. I bought a generic one from my sewing center at Joanns. It did NOT fit my older machine. Just make sure returns are possible.
HTH, and good luck :wink: