It's not the most desirable method (and I apologize if I'm stepping on any toes), but you could close this account and create a new one with the username you prefer. You just recently started playing, so it's not like you've got an inventory full of clubs & credits you'd be giving up, and you haven't gained the experience necessary for people to call you a cheater after you come back shooting in the 50's with starter clubs.
I'm not sure if there's a grace period between uses of e-mail addresses though, so if you're dead set on changing your username, it's something you may want to inquire about beforehand.