Be yourself. If you want her to see you as you, you need to talk to her without any lies. If you're not an outgoing person, she needs to know that.
If she doesn't like you that way and can't accept your feelings, don't just decide to avoid her for all eternity because of your wounded pride. She's probably very nice (you'd know, right?) and would make a lovely friend.
(But also, please try to remember that if she doesn't like you, it's neither yours nor her fault. She's not obligated to like you. You're not immediately less of a person just because your feelings weren't accepted. She never asked you to feel that way about her and you shouldn't automatically expect anything from her, but also remember that you are not a loser if she rejects you. You're probably an awesome person; you're not unworthy just because a girl doesn't like you in that way.)