No, you haven't undone seven weeks of good work. You just had one bad day. Let's look at this objectively:
There are 49 days in those seven weeks.
You had ONE bad day.
If you break that down that means a TWO PERCENT
stuff up rate!
I WISH I only slipped up two percent of the time! I'd probably be at goal by now if that were the case!
The best thing you can do is look at this as a blessing and not a failure. Did you slip up? Perhaps. But you're still committed to a healthy lifestyle so it's better to slip up now than when you've got to goal and you don't care so much. Because then the binges start adding up without your noticing and before you know it you've regained your weight again.
Use this incident to help your weight loss journey! Getting to goal and keeping there isn't just a matter of food and exercise, we also have to learn more about ourselves and why we gained weight in the first place. Why did you run amok in the snack bar? Was it out of habit? Was it a reaction to feeling deprived for so long? Once you figure out why you did it work out a solution that will prevent the problem from reoccurring. If it was out of habit is there any way you can break that habit? You could force yourself to go to a couple of movies on your own (no peer pressure) and not have any snacks at all. A movie is only 90 minutes long. It's not like you need rations lest you starve to death before the credits roll! If you were feeling deprived can you work in little treats along the way? And if it's just the fact you like eating during a movie can you substitute unhealthy snacks with healthy ones?
Good luck! I'm sure the scales aren't going to be as mean to you as you fear!