How do I fix my round off? Cheerleaders and Gymnasts Only!?

I've been in tumbling for almost twelve weeks. I can do back handsprings, back tucks, and front tucks with a spot. I want to learn how to do a round off back handspring, but my round off landing sucks. My legs don't seem to snap together in the air. I've tried everything. I tried doing cartwheels into hand stands and landing on both feet, but nothing is working for me. I was wondering if someone can tell me what I can do to get my landing together before I move on to attempting back handsprings by myself. I want to get this down by August, but I really need help. What can I do to fix this problem?