Backhandspring Help!?

Hi there! I'm sixteen and I'm going to be a Junior in High School! I am currently on the JV cheer squad! (: For Fall Kickoff, the seniors are making me do a backhandspring! I've been able to do one with a spot but never by myself! I have to get it before August 19th! Does anyone have any good tips and I will be taking once a week lessons! Is it possible for me to get it and should i work on arm muscle? thanks so much!!