Could I go to jail if I had sex with an 16 year old and I'm 18 teen but she always made the first move on me and she thought she was pregnaut and told her parents that I wasn't there to help her and every time I was she would just blow me off

Depends on where you are at, but in many states yes, she can agree, ask for it, pay you for it, but if you have sex with her, you go to jail, and are on the sex registery forever.

Now in some places Canada, many places in Europe, it is OK, and some states in the US. But in general best advice is no don't

To add to what Chuck said... if she shows you a fake ID showing that she's over 18, and you get that notarized, with the signature of a dozen witnesses... you still go to jail when she turns out to be underage. The law is that strict.

What state/province/country are you in? We can get you a more definitive answer with that information.