This guy and I like each other a lot. We were supposed to hangout at six but he didn't respond back to me till 6:30. When he finally did reply he's all like we can hangout later tonight I'm going to do a few things. Is he blowing me off or am I just overreacting? Idk how to respond back to him because I'm just a little mad but I don't want to blow up on him.

I would not respond at all. It's really rather rude

You like each other a lot or you like him a lot? Yeah, without good reason, what he did was rude as HG said above me. I might consider blowing him off if I was you.

Probably something came up? You can give him a chance

When you calm down you can listen to what he has to say and then judge for yourself what you do about it.

I agree with Tal. Calm down, and when he calls, or texts, or whatever, and you two meet up, ask him why he made plans with you if he had other things to do.

If you did not hear from him, why did you not call him?

If you rely on messages, they don't get though, people forget them.

If you want to make real plans, do, so by talking to the person.

Most likely he is blowing you off. So, now the best for you would be avoid coming out that night. Tomorrow ask him to explain the whole thing to you. If you did not like the explanation, turn around and look for someone else to date.