Even the attempt to have sex with another person is a crime. If you do say no and the other person will not leave you alone, get away as soon as possible.
Rapists choose victims who look or who are vulnerable.
So remember, if you have been raped, it was NOT your fault, you didn't ask for it to happen. If you are a victim, you need to talk about your feelings with someone you trust and who will listen to you. If you were just raped you need to see a doctor as soon as possible, you could contract a sexually transmitted disease or become pregnant. Do not take a shower before you go, this will destroy evidence.