Welcome to the board from Southern California!
Do you have a walking foot? It helps. If you are doing free motion it helps to have a consistent speed coming around the curves. You may want to hold your project so that you pivot the project around where you are holding. Does that make sense? Kinda like when you learned to use a protractor to make a circle, the point is held still and you pivot around it. It takes practice. My quilting is not the greatest, it's hard to keep your stitches consistently the same size.
Practice, Practice Practice!!!