You know...I wasn't afraid of double flyaways and salto vaults. I could actually pull them off on the first try, but I had a hard time doing them "right", and adding twists and changing to a layout position.
Later in my career, when I was too beat up to compete, I was sent to a tramp/tumbletrack to learn basic tramp drills/skills, and it really helped me understand and control rotation.
Double flipping backwards (which is basically what you do once you turn your body around in a half-on) is a double backward roll in the air.
As lame as it sounds, see if you can do two backward rolls in a row. Do you get stuck in a headstand with your behind in the air? That would be the symptom of a lack of experience/understanding of backward rotation. A gymnast can get away with poor rotation doing a layout on floor or a handspring vault, but double flipping requires more advanced rotation.
Can you do a back 1 1/4, pullover to your feet on a trampoline? How about a back 3/4 to your stomach, back 1/2 to your back and a pullover to your feet? Double back on tramp, off of a minitramp into a pit? Double fronts anywhere?
All of these drills can help an athlete become more comfortable with rotating. If you are afraid, you may have good reason, especially if you aren't clear on what your body needs to do to achieve the right amount of rotation.
Good luck!