Nicholas, thanks for posting this question. It's definitely a good idea to explore as the next season of life approaches for you. Yes, your English teacher is right on the mark - make your essay about you, not about what you've done in terms of accomplishments and various awards, but more about your character. If I'm a college admissions office, I want to see who you are in the best way, even if you've made some mistakes. How did you learn from them? What prompted you to get where you are now? What obstacles did you face along the way? Give me an example of something you did that surprised others. When you provide a deeper narrative about a specific moment in your life that changed or affirmed who you are and what you're capable of doing, I'm very interested in what else you can do!
Best of luck! Matt