The friend zone genuinely and honestly does not exist. Don't worry about it.
I've seen people who have been friends since INFANCY who end up scoring. Trust me the friend zone is not real. She either likes you or she doesn't. The amount of time you've known her is not going to affect whether she likes you or not.
The only problem is that girls use "friend zoning: as an excuse not to directly reject someone. I think that's very unfair, but "let's just be friends" is NOT saying that she doesn't want to ruin the friendship, it's saying that she thinks you're unattractive and is too cowardly to just admit it up front. But the "friend zone" doesn't exist.