how Can I fix this day and discipline myself not to overdo it again?

[princess17]

I diet all week which means no junk food at ALL! I don't drink soda ever not even once a week, nor do i eat ice cream n chips. But once a week i have a cheat meal and that day was today but since i was out the whole day, this cheat meal became a cheat day and i over did it, i ate too much junk food, how can i fix this? Prom is coming up and i want to look good! please help! I am also in a sport in school which means practice 5 days a week. How can i discipline myself to one cheat MEAL once a WEEK?