I like this girl, so I asked her out to the dance and out on a date. She said yes to the dance, but when I officially asked her out, she said I don't know. I said anything I can do to change that, she said I don't know. What does this mean what do I do?

It means you are OK to go to the dance with but you're not OK for anything more... yet. So, you go to the dance with her and prove you're fun and worth dating.

Take her dancing again, and have fun. I think she was trying to slow you down because you are moving to fast. More dancing dates are required before you can get the official stage. Or she only wants to dance with you, and no official dates. IDK, either.

Depends on girl.I think it'd be two ways of I don't know.
№1 she wants you to be more attentive to her,to try more and deserve her attention.
№2 she's trying to be polite to you and her I don't know means no,but she's not enough strong to tell you no...

What do you mean by "officially" asking her out, do you live in a culture where you have to do it though her parents ?

Asking her to a dance is "asking her out" Did you already do the dance, did you ask her out again after the dance.

You don't ask a person out for several dates, you ask for one, then wait till that is over to see about next one.

My experience says definitely NO :-( I'm sorry about that.

I don't know means 'no'. She had a change of heart, which usually means she was not that enthusiastic about going anyway. Would she say "idk" if it was someone like Brad Pitt? Sorry man...