A heretic is a person who subscribes to or believes in a Heresy.
Really? Would that be regular toasted or extra crispy?
Note that you probably didn't see yourself or refer to yourself as a heretic. You were just another good christian, such as one of the Lollards, the Hussites or the Cathars. Remember that heretic was not uncommonly used as an insult to be used against anyone who basically disagrees with your own religious viewpoint.