Wow, that looks like one of mine! Here's what I learned that I was doing:
1. I want to go too fast. I really have to concentrate on moving steadily and consistently
2. Stippling shouldn't cross over itself. That's what keeps it from looking "messy"
3. I use my walking foot, rather than FMQ for all lines and even gentle curves like the ones you did. It makes them smoother.
4. Mark your quilt tops and try to follow the lines.
5. It takes practice, practice and more practice. I still have practice sandwiches that I use to help me "set the motion memory" before I start on the real quilt.
Good luck.