It'll be okay, hun.
You said you didn't want to know the calorie count for the pizza, so I won't say, but I'll reassure that your whole binge cost you 3500 or less. Like EmLay said, one meal won't ruin your weight loss. I'll wager that just about everyone who has experienced any significant weight loss has slipped up or had binges before! I know I have, but I get right back on the wagon and then I start losing again.
Depending on your normal daily calorie deficit, it may only take you a few days to negate the binge calories so that your weekly average is at or below maintenance. (Don't stop eating or go to an extreme calorie deficit!) Just do your best to make your next meal healthy, and then the next, and so on. Don't step on the scale right this instant, but wait a few days for things to level out.