If you requested the day off, and put it in a request time off book or w/e your job has, then you should be fine. I wouldn't go in, and if they call, you tell them that you took that day off and that you didn't see the "new" schedule if you're worried about getting fired.

I think that's really fucked up though, how they change the entire schedule AFTER it's been made. If they need to switch people or have you come in an extra day, they should be asking, not doing it w/o asking.