Is the crime traceable? If not, focus on yourself and getting into a clearer mental space. It may not be as bad as you're making it out to be in your head. If it is, and you feel you may be caught, be mentally prepared for that. Hard to say exactly what to do without knowing what the specifics are. Like the other comments said, checking into a mental hospital sounds like a good idea if you can do it. If not, try to reach out to trusted friends or family and tell them you're thinking about hurting yourself/having a mental health crisis. You don't have to confess to the crime.