I worked in a film last year and I did it voluntarily because to my knowledge I'm not supposed to be paid by non other than the university. They made me sign some documents because international students do that all the time. Now I got a W2 Form that says that I got paid, but I didn't. Now I don't know if I'm in trouble.
Yes you may be in trouble. While non-work visas permit some kinds of volunteer work, one of the restrictions is that you cannot do work that is normally paid, even if you do it for no pay. The existence of The W2 indicates that the film company thought this was work that needed paying. So there are bigger problems here than just whether you got paid or not.
I would talk quickly to the film company and the university, and you might consider consulting an immigration lawyer.