How to not be scared to do a backhandspring?

My neighbor is really cool and she was a cheerleader. I need to learn how to do a backs-handspring so I can definitely make my schools cheer leading squad. Im so used to doing it in the gym that now whenever someone tries to spot me I just freak out mid-flip and fall straight back! I need to learn how to do this in the next few days. Im so close to being able to do it!!! Please leave tip on how i can feel more comfortable doing it in my backyard with a new spotter. But i dont want comments about how i shouldn't be doing it in my backyard because my coach told me i could but i can go back to my coach anymore because my lasses ended.