I need some advice. (KIND OF URGENT)

Okay, so a few weeks ago I (f15) met a guy (18M) at the resource room at my school (Special needs space/computer access classroom). It seemed pretty fine at first, but after about a week he started hitting on me just kissed pretty suddenly (Kind of shitty sitch for my first kiss, but whatevs), but I really just don't see him that way. I tried to hint that was into him, but he didn't really get it, so after a couple days I just straight up told him that "Hey, you're a nice dude, but I'm really just not comfortable with this, so could you please cool it?". He took it pretty well at first, but after a few days he started trying to kiss me again and asking if we could go to second locations alone. I said no, and repeated again that I'm not interested, but he won't leave me alone now. I can avoid him, because I have to go to the resource room in the morning to get my computer, and he's always there to (Even if I get there literally an hour before school). One time I finally got there before him, and so I got my computer as fast as I could and went to class, and found him God damn waiting for me there. Turns out, he's basically memorized for first classes of the day and is now just following me in the morning. And yesterday, he somehow got my email account and has now been sending me explicit material that I'm really uncomfortable with.

What the hell do I do? I don't know how to handle this and I'm not sure if I should be scared or something?.. I just don't know if he'll stop.