I don't know about official consequences, but you'll definitely piss off your supe. If you told them yes, go. Don't be that person. Unless you have some kind of emergency, then call and let them know ahead of time.
Since you said yes it is definitely not a good idea to pull that. if you need to call off like if your sick or something call and let them know. its just a douche move and since you said yes they probably could count it as a no call no show.