Is it rape?

When I was 16, I had just gotten with my first "serious" boyfriend. I had already lost my virginity to him, and he wanted me to meet his mum. I went over for lunch at his house, an when we'd finished we went up to his room to watch a movie. He wanted to have sex , but I was fine just watching the movie, and whenever he asked I said no. Eventually he undressed me and we had sex, despite me saying no before hand. I didn't fight him off, but i still think about it today. I guess I just need to know whether or not it could be considered rape.

Sorry that happened to you. The issue of rape depends on consent. If you didn't consent to sex, that would be rape. If you consented, then it would not be.

The circumstances you describe happen often and just as often, result in a he-said, she-said difference in viewpoint. He might feel that you did consent, while you might feel that you didn't. It can be hard for an outsider to define. You would know what actually happened, so you would best be able to say whether you consented to his actions. Again if it was non-consensual and you were an unwilling participant, then that would be rape.

At a minimum, he should have respected your choice and not pushed any further. When people don't do this, they are crossing a boundary, and then their only hope of not committing an assault is that the other person does consent at some point. It's a risky and stupid thing to do, but as I said, common. A better approach is to respect the other person's right to make that choice for themselves, and not make any attempt to force the issue. No means no, yes means yes.