These things happen.
None of us are perfect, and we all make choices from time to time that aren't good for our waistlines. Even the best dieters screw up once in a while and go off plan.
Just this weekend I overate at a barbecue (burgers, chips, cookies, etc.) and gained a solid pound. I could have just said to myself, "Hey, I gained 1 pound back, I might as well stop trying to live a healthy life and gain the other 62 pounds back too." But I didn't. I accepted the fact that I overate, and then moved on. I'm too happy with my progress to give up now just because I ate like a piggy for a day.
So you overate... accept it, and move forward!