It was a shaky way to start in the first place, that question. I think you need to talk to her. If she likes you, and you like her, then it's not like she'll turn you down. All you have to do is say hello to her.
Dear lord. Sounds like some kind of day. Alright, well, lets start with the whole being depressed thing. So, you're depressed, because you fancy a girl, and she fancies you, but you can't gain the nerve to make a move?
C'mon, you're fine. You didn't do anything to disappoint her, it was the teacher. Despite how corny this is about to sound, letting out your problems and recalling the emotion is another way of letting it out, which will make things easier to bear.