Legal Question in Administrative Law in California

I assume you mean for statutory rape. The criminal act does not disappear merely because she turns 18; if charged it would be for what you did in the past, not the future. The greater the difference in age, the more likely the police would arrest you. You have put yourself in the position that your girlfriend and her parents can blackmail you with the threat of going to the police on the rape charges. They probably are well aware of what has been going on, but if they get angry enough at you they could go to the police [especially if you co-produce a baby]. She should gently try to find out what they know or believe about your relationship and then calmly state what your relationship will quickly turn into. The less they suspect of what you have been doing, the more upset they will be [and they should be upset as you should not be fooling around with a minor; if before she tells them you propose marriage, you are safer.