it could be a simple fact of him not quite understanding the intensity of going to university.

I may not have gone to a university myself, but I do know they are quite demanding- and it could be a case of well... all my friends are going to one, I want to go to one too (teenagers are like that)

I'd just sit him down and explain things, ask what he's anxious about, and try to give him encouragement related to that anxiety.

you can't force him to go to some event he doesn't want to go too, true,, but if you help him understand why he's anxious, you could help him go to it (and if the event is a one day thing, stay with him during it)

and if he doesn't go, yes, you've lost all that money you payed to have him go, but also he has to decide his own future, his own path

maybe he's not ready for certain asspects, and that's okay