I'm planning to break up with a girl a couple days after we hooked up.
Why would you do that? Do you think that she might think that you led her on?
Well, I just don't want to be together with her. She's not my type.
If you are sure about that, I guess. I think that it is going to hurt her a lot. You should not have hooked up with her if you knew that she was not your type.
It's okay, she'll get over it.
I'm sure she'll get over it, but that doesn't mean it's a nice thing to do. She'll probably be really upset with you for a while. In the future I don't think you should get together with someone if you don't really like them.