Question: Do I need to join a sport?
We assume that what you're really asking here is if your chances of college admission will be diminished without a sport on your record, right? The answer is definitely not. It is a big plus to play a sport if you are good enough to interest college coaches so that they lobby in your favor at decision time. However, the vast majority of high school athletes are not in that category. It's even a big leap to move from a high school team to a Division III (the lowest NCAA level) sport in college, and usually only real high school stand-outs make that transition successfully.
In most cases, admission officials regard athletic participation as a valuable use of one's time, but they don't view it as a big "hook" in the admission process unless a student is qualified for their college team. Thus, any passion you pursue now--athletic or otherwise--will be considered an equally valuable use of your time, and you should not force yourself into a sport that you don't enjoy just because you think it will "look good" on your applications.