As far as activities go, the best bet is to get involved in what you’re interested in outside of school. Rest asssured, many kids get into amazing colleges without ever playing a sport.
Colleges won’t be interested in the reasons you don’t have many extra curriculars. If you’re the type of student who is talented enough to attend a top college, you will make your opportunities happen. If you like sewing, sew quilts for senior citizens or homeless shelters. If you love to cook, get some friends together, start a cooking group, and teach yourself how to make exotic foods. If you’re interested in gardening, get involved with a community garden. And then go beyond that.
Offer cooking classes to little kids, or donate prepared meals to families in need. Arrange a zoom session with a quilting instructor using donated/collected cloth scraps to make quilts. Grown vegetables in the community garden and distribute them to food pantries.
If your school doesn’t offer much, you need to think outside the box. You can of course create your own after school club. Find out if there is any money in your school’s budget to encourage a teacher mentor. (Teachers are often given a small amount of money to head up such clubs.) A meeting with your guidance counselor at school could be a first step to that.
It might be a good idea to put aside your “dream school” ideation for now. Who knows how astronomical college fees will be in three years’ time. Unforeseen circumstances might arise. It’s much better to think “Northwestern would be great, but my goal is to graduate college with a hard-earned degree.”