Listing the major scenes that need to be a part of the story will help you get organized and find a good place to start. You don't need to write up a formal outline for a narrative essay unless it's part of the assignment or it really helps you write.Does it start when you spill spaghetti sauce all down your dress before the dance? While that might seem like the climax of a story you want to tell, it might make a better starting place. If you want to tell the story of your prom night, does it start when you get dressed? Maybe.
Where does that story start? Not the first day of school that year. While it might seem like we need to know a bunch of specific details from your senior year, try to think of a particularly tumultuous day from that year and tell us that story.