WHY DID HE HESITATE WHEN I ASKED?

[cupcake]

What's WPA?

edit- oh ok
If you're a freshman in high school and so is he, I would assume you're both about 14-15 years old.
A 14-15 year old boy doesn't have a lot of dating experience and possibly lacks "social" skills when it comes to girls.
It's very possible he was surprised that you would want to go with him, since you're very cute, which made him hesitate. He could have been confused, figuring you two were just friends, so he was surprised that you'd want to go with him. His hesitation may have been him thinking "does she like me?" Then when you added "just as friends" which could have confused him more.
He said yes.
If he didn't want to go, he would have said "maybe" or "I'll think about it" or "I'm not sure if I'm going" or "I'll tell you later".