Mental block in tumbling!?

I have a huge mental block. I won't do my backhandspring because I'm scared... but I have no reason at all to be scared I have never done it and not landed it. I just watch other people come close to not landing it so I get scared that I won't. I will do it on a squishy blue mat and a cheese mat but not on the floor. The blue mat is actually harder then doing it on the floor. This has been going on for months and sometimes I will do it on floor and sometimes I won't. My coach thinks it's getting ridiculous so he won't spot me for it anymore. I need serious help like It's jsut a backhandspring? I have no idea why I won't do it. Any tips...?