@jenniferkro,
It sounds to me like he's distancing himself from you. A formal is more of a big deal than a regular date. Why not ask him out on a date? Something small, and not so fraught with meaning. If he says yes, then maybe consider progressing to asking him to the formal. If he says no, then you know where you stand.
Oh, and if the formal is tomorrow - don't ask him to it.