Fucking do it. This could in fact be your only chance.
"pay" your school for time off? lol sounds like bribingplus stop saying star :c if you're an extra you'll literally be walking around in the background lol, it would be cool but it's really not worth derping on an exam just to walk around and get on screen for 5-10 seconds
As people said, once in a lifetime. You should do it, 4 days really isnt going to hurt you that much, heck you could use one weekend to catch up if it really is that important.Of course, this is only once in a lifetime unless you're going to become an actor one day.