But you said you were going to spend the 4 hours sleeping. Some grandson...
I'm still not buying it. You admit you've never been to one and insist you aren't going simply because you are too lazy to do so, not that you don't want to. You are probably taking 'afraid' too literally. I would argue that given the circumstance that you happened to be right outside the dance, didn't have to pay, and noone at all had any dates so you wouldn't feel out of place in that regard you still wouldn't go.
If you didn't go under those circumstances it would be a classic case of anxiety towards a situation outside of your 'comfort zone.' If you were really 'just too lazy' then you would go to the dance in the above hypothetical situation, but I don't have any reason to believe that is the case.