How to make my round off back handspring stronger?

Ok, I am a 8th grade captain for my team and so of course I want to make a good impression for high school cheer next year. I can do a standing back hand spring and a round off back hand spring at my gymnastics and a standing on the floor, but I tried my round off backhand spring at cheer practice yesterday, (on the grass) and I like fell on my knees. That was the first time I have ever done it on the grass without a spot and I might of freaked myself out. But my coach told me that I HAVE to tumble during my starting lineup. Last year I did a standing and HATED it, and I only did that because I refused to do a round off backhandspring. So I am a little worried I will mess it up and make my team look stupid. What can I do to strengthen it? Or make sure I get a good rebound? Any answer acceptable. Thanks! Cheer on! *\o/* :)