This girl is not into nice guys (like you) right now because that's not what a high school girl wants. She wants an asshole because she doesn't have the self-awareness or self-esteem to know or want anything else. She wants the jocky dickwad who's "hard to get" because it's a challenge, and immature girls want a challenge.
They don't understand the "good guy" and the value of a super-nice and sweet guy until they actually look at themselves and are like, "Oh, wait. Being treated like shit actually sucks. I'm not going to stand for that nonsense anymore." You have to get dumped on a LOT before you change your ways. Such is the way of the world.
She's not there yet and it could be a long, long time before she is.
I don't know if this girl likes you or not, but it seems like she definitely isn't looking to date, at least for right now. It sounds like she's probably confused about her feelings. She's 18, that's pretty normal.
Friend zone? Maybe not. She's definitely not interested. Eighteen-year-old girls are boy-crazy and she'd be all over you if she were down. I wouldn't think of this as "giving up," but more as just accepting reality, even if it sucks and you wish it were different.