Come out to your boss and try to reach an understanding. Let him know you're unsure if you're ready to be full time, but that growing your hair out is part of your process. The good thing is they couldn't fire you for that if they already know because it's discrimination and would be a lawsuit waiting to happen, but the bad thing is they may look for small reasons to let you go. It is a rough spot to be in, but I think you'll be okay.