The best way to improve your free motion quilting is to practice on a practice sandwich but another way is with paper and pencil. Get a blank sheet of paper and a good pen, then mark off the area you will be filling: for example an eight inch block or a four inch border.
Then practice the filling pattern you plan to use. Be sure to draw with your whole arm and not just your hand and wrist. This way develop a little muscle memory and you can troubleshoot your design before you commit your pattern to fabric.
As you can see in the photo, there’s a lot of practice needed in the future before committing this to a quilt.