What to do about CREEPY guy?

This kid (let's call him Tim) was in my 5th grade class. We didn't talk in middle school, and now, high school, we're in 2 classes together. We sit together in both (assigned seats). We talked, but only 2 or 3 times. My best friends (let's call her Cara) told me to be wary because he'd asked her out before.
I gave my number to him a few days ago. Then last night he texted me. He asked me if I used FaceTime. I got a little creeped out and said no, lying. He told me he'd wanted to ask me something. I ignored it and went to dance class.
Almost 30 minutes later I pulled out my phone to show Cara what he'd said. I turned it on (iPhone) and there was a new message from TIm: "Do you want to go out with me?" I squawked like an ostrich and replied, "Sorry, I already have a boyfriend." He said, "Oh. I didn't know. We cool?" I said, "sure."
Later, he asked if he could ask me 2 questions. I agreed. He asked me: "If you weren't dating, would you say yes to me?" I awkwardly replied: "Um, I don't know." Then he asked, "Also have you had your first kiss yet?" I was totally creeped out by now, and I said, "yeah… Why?" And he said, "Just curious."
He keeps asking me creepy questions and texting me constantly. He won't leave me alone. Like somehow he found out that my dance classes today ended at 9, set an alarm, and texted me at 9 on the dot. He also says, "text me when you get home." He still thinks we're close! I'm weirded out, how do I tell him to leave me alone?

Added (1). Also, I told him I have a boyfriend! He shouldn't be asking me if I've had my first kiss yet or if I'd say yes if I wasn't dating!
AND he tried to guilt me into saying yes by saying, "I've been rejected 7 times and all the girls I like (like you) are taken or say no."

Added (2). 1: I tried not texting him. It didn't work. He came up to me later in the day and asked me why I wasn't answering him. I told him because I was in class (true) and he got mad.
2: I don't think you get it. I don't care if he likes me, whatever. I phrased my question wrong: I don't need him to LEAVE ME ALONE, I need him to give me a little more space. It's been 4 years since we talked and we're not close like that yet. That's what I meant.

Ohh yes totally creepy he likes you i can't think of anything worst ---- call the police have him arrested ---- he can't like you thats illegal ---- i trust you can hear the sarcasm? ---- why not do something totally outrageous ----- tell him the truth ---- that you don't like him you don't want to go out with him --- don't lie don't make excuses because all you are doing is leading him on ---- he will think maybe just maybe at some point you will say yes if he asks you out
you ladies go on like this and then wonder why guys don't approach you

Um you do know you don't have to keep texting him durrr. Just ignore him. Don't even talk to him at class.