Keep in mind that a narrative essay is simply one which tells a story. The prompt to write about a remarkable day in your life means this is a personal narrative.
My best advice for you on this essay is to free-write a journal entry first. To do this, think about what day you will write about. Sit down for 10-15 minutes and just write, anything you can think of. Write about what happened, include your thoughts and feelings, and be sure to put any specific details you remember that might make your essay more interesting. Keep in mind that this is a free-writing exercise, which means that it does not matter the order in which your thoughts come out, it does not matter how they sound, and it does not matter if any of it is technically nor grammatically correct at this point.
NOTE: This free-write is not a rough draft. It will not be turned in. Hopefully your final draft will not closely resemble it either.
Instead, use this "free-write" as an exercise to get all your thoughts on paper. Then, organize them. Re-read what you've written and determine what message you wish to get across by telling this story. Do you want to share something humorous? heartwarming? a lesson learned? something sad? Keep in mind that it does not matter what the point of your narrative is, but it must have a point. Using your "point" as the main focus for your essay, you can determine which details are necessary to your story and which are not.
It is usually easiest to organize a personal narrative chronologically. If this works for your essay, go with it. It will help you stay on track. Think of your "remarkable day" in terms of beginning, middle, and end. Use an outline or graphic organizer to put the details of your essay into these three groups. This could very easily be the basis for your body paragraphs.
Once you have the bulk of your ideas visually organized, you can turn them into paragraphs. I suggest writing the body of your essay first. Then, the introduction needs to only introduce the main point of the essay and does not risk summarizing several details which will not be included. Your conclusion, similarly, should leave your reader with a final thought or feeling which ties back to the point of the essay in the first place.
Keep in mind that personal narratives allow you to include personal thoughts, feelings, and emotions. Also, they can be a little bit more creative than a typical expository essay. Despite this, they still must have a topic/focus/thesis, thoughts must flow in a logical way, and the overall essay must be organized in a way that makes sense.