A college admission essay is not like an ordinary 500-word essay. It is about you. You have to write down about your qualities in a way that leaves a positive impression of the reader.
Your college admission essay should showcase your personality other than your academic grades. The professor reviewing your admission essay will not be interested in reading about your grades in it. He has your transcript for the same reason.
Write about yourself, about your qualities in your essay. Don’t try to explain everything about yourself in the essay. That is not possible to explain your life story in a few words.