The typical prompt or assignment for the narrative essay will ask you to describe an event that affected or changed your life. In other words, in the narrative essay prompt, you are being asked to tell a story. Because of the basic structure of this assignment, students are often fooled into thinking that the stories that take place in a narrative essay have to be true, which often becomes a source of anxiety. "How can I write about myself in a way that will interest my professor?" you might find yourself asking. "After all, nothing interesting has happened to me. And even if something interesting has happened to me, I'm not sure I want my prof. to know about it."
The best way to address this concern and start writing a narrative essay is to forget about telling "the truth" or "the facts" of a story unless you already think those truths and facts are interesting. Along with telling a story, after all, you're also being asked in the narrative essay to write vivid descriptions of persons and events. What if you don't remember what one of your characters was wearing or looked like or smelled like on that fateful day when you decided to skip school, or become a young Republican, or sneak out of the house to party with the very boyfriend/girlfriend you broke up with a week later? The answer to this question is that it simply doesn't matter whether your descriptions or events are "true to life." You are, after all, telling a story, and stories - even autobiographical ones - are embellished with made up details, characters, and events all the time.
Once you know the point you want to prove, you just need to provide supporting details, whether real or imaginary, that make that point stand out. If these details are believable and related to your narrative essay's purpose, it simply doesn't matter whether they actually happened. English class isn't a court of law, after all, it's a chance for you to extend your command of the English language. As long as that's happening, you can feel secure in almost any story you decide to write.