It's not too late to get involved in an extracurricular activity. Even if it's something that does not require a lot of time. Choose something you enjoy and get involved. Book club, school club, town recreation sports, an hour a week adds up by then end of your 4 years of high school. If you choose something you're passionate about, you will have a lot of good material to draw from when it comes time to write your U of Chicago application essay.