Great job stopping at one, take this as a learning experience. Next time you see a donut you might think twice about eating it, was it worth the aggravation and guilt? If it was, plan for it next time, if it wasn't, skip it and plan for something else you really want.
Sometimes, I'll look at what the points are for something like a turkey sandwich with one piece of cheese on whole grain bread (about 7) and compare it to a donut (easily 7) and think what is "worth more" what is going to satisfy me more?
best of luck