If you stopped showing up to water polo practice, would it make a difference? Would your absence be noticeable? Would it negatively affect the team?
If you're a great player or the team captain, the answer is probably "Yes." But even the kid who sits deep on the bench can still play an important role, one that would make his absence noticeable. We worked with a student years ago who told us he was, without question, the worst player on his water polo team. He'd played a total of about 3 minutes of actual game time in high school. But he loved the team. He brought a great attitude to practice every day. His passion was contagious. That's why he won the coach's award two years in a row even though he never played.
Making a difference means that something or someone is different as a direct result of your involvement. Successful college applicants consistently make a difference. They make their English class better because they participate and ask questions. They bring energy and enthusiasm to their activities and improve the experience for everyone involved. When they do community service, or take a summer class, or take a leadership position, they're not doing it to impress colleges. They're doing it because they want to make a contribution.
If you want to improve your chances of getting into college, find more ways to make a difference.