Its simply claories in and caloriues out for weight loss. How much extra did you eat? its 3500 calories for 1lb of genuine weight loss, so soemthing like 15 mars bars, 2 pizzas, 2.5 big mac meals. Weight loss inst linear so it might have minimal effect, it also depends how overweight you are.
Dont demonise food. You ahve a right to enjoy yourself on your birthday, so dont sweat it. Try and get back to controlling calories again after, but beating yourself up is utterly pointless. In most of thes situations people grossly exaggerate and think the sky will fall in. It will not it will just take you a few days extra to get to target.