so i asked her out. She said IDK.

Okay i like this one girl at school. The only time we talk to each other is when we transition to another class period like 2-3 minutes( between 1st period and 2nd period ).

We flirted sometimes during that period, for example, she would tap my shoulder and hide, leaving me confused in the hallway, and I would do the same to her the following day and after that, we would start to talk.

I don't really see her a lot during lunch or break because we hanged out in different areas. She's usually with her friends. She's very quiet, shy, and sweet.

So then I decided to ask her out in person after school. She didn't really gave me answer, and I can tell that she's nervous. She took one step away from me and smiled and looked around awkwardly ( onto the ground and then to my eyes again, then back to the ground ) and murmur squeakly " I Don't Know". After a few seconds of awkwardness, she changed the subject, and we continue to talk until her ride came. She smiles and said "good bye, i'll see you tomorrow 1st period.", waved at me and walk to her ride.

So........ now what. What doe she mean "I DONT KNOW"? What should I do?

Congrtulations on asking her. Now you need to follow up. The way she said IDK means , "I feel a little uncomfortable and shy right now." If you treat it like a big deal and act hurt or don't mention going out again she will think you can't handle her shy ways.

My suggestion is to ask her out to something SPECIFIC. Make it shy person friendly. Think of the least thretening thing the two of you could do togather. Think no pressure. Once she settles into the same comfort level she has with you in school out of school THEN you can think about more formal dates and making moves. Shy girls can be a bit tuff to crack but they often make the best girlfriends once they open up.

I agree you need to follow up. She IS interested, but you need to find an activity to do together (ie: zoo, museum, basketball, or whatever she's interested in). Make her comfortable and she'll open up, if only slowly. Don't put pressure on her and let her show you who she is in her own time. Good luck!