Why did you put this under martial arts? Backflips have no place in fighting. Regarding your question though, just try it on a trampoline. If you're still scared, I suggest you man up.

do it in a pool first.or on the soft surfaces of gym.

I suggest that you go take gymnastics.

When my friends and I go to the rope swing they all do backflips and some even double backflips. Then when I go up to jump I know what to do and how to do it but I cant go for some reason i get to scared. Although when im watching my friends do it and even now I know I can do it and thats really pissing me off. Then, when my mood completely changes as soon as its my turn to jump. What can I do to get over my fear and just go.