was this sexual assault?

I was over at this boys house and things were okay and relaxing then all of a sudden he wanted to have sex. we've had sex before so that wasn't the problem it's just that I wasn't in the mood and didn't feel like it. I told him I didn't want to but he kept trying to get my pants off and when he was able to get them off and put it in, I kind of just gave up trying to get him to stop when it wasn't working and he didn't seem like he wanted to stop. am I over thinking this or no?