You say you are still in school. Most love doesn't happen in school, and it is probably just an infatuation.

You can't literally MAKE a girl fall for you. You can't control her emotions and if she doesn't feel that way for you, then that's not going to change because you're working your ass off to get her to notice you more as a boyfriend instead of just a friend.

What do you mean, "once I'm gone"? do you mean you're leaving? If you are, then it probably isn't a good thing to try and "make" her fall for you. If she does fall for you, then when you leave, she won't understand why you did that to her. It's like a hit and run.

When you flirt with her, and she pretends not to notice, it's most likely because she doesn't like you that way, and she doesn't want to pretend she does, and have everything be awkward.

She is your friend, and if you honestly can't handle that she doesn't want to be your girlfriend, you don't even deserve her as a friend.

However, if you're absolutely sure you still want her to fall for you, despite everything I just said, here is what to do: First, just be yourself. I know that is very cliche, but it's true. You shouldn't change yourself. Next, make her laugh, ust like you've said you've been doing. Also, be sweet. Maybe she'll come around and see how caring you are. Don't become her slave, though. Unless she is a stuck up snob, she probably likes to be treated as an equal.

Note though, that most friend-gone-dating relationship end in them breaking up, and then everything is super awkward.