If I'm trying not to be bulimic but I overeat one day, what should I do instead of throwing up?

Talk to Therapist. If you have an eating disorder, you should really be under the care of a therapist who specializes in eating disorders and discuss with him or her, appropriate strategies to prevent binging in the first place.
What do you mean? "overeating" is best confronted with the help of a doctor. You may think you are overeating. But, in fact, you may not be. You have to work closely with a medical professional to understand what your actual caloric needs are, what your "ideal" weight is, and what your goals should be -- not what you think, or "feel, " they should be.