My girlfriend of 3 years won't have sex with me

My girlfriend and I have been dating for 3 years in December. I am in college and she is a senior in high school. When it comes to our sexual life, the only thing she will do for me is give me handjobs, which is seldom. She will not give a blowjob or have sex and stuff like that, just handjobs. I, however, do everything for her besides sex. Go down on her, fingering, etc. Over the past 3 years, I have brought up sex many times, but never pressured her to do it. I think I have been a VERY patient boyfriend. Whenever I ask her now if she would give a blowjob or have sex, she says she isn't ready yet and is scared. We have been dating for 3 YEARS!!! I think that it is time that we can move to the next step. I go down on her, the least she could do is go down on me. And I think waiting 3 years to have sex with your girlfriend is being patient and she should be ready. Am I right in thinking this way??