Is it bad that I'm doing most of my activities only junior and senior year?

I wasn’t really aware of a lot of clubs and activities freshman and sophomore year so I didn’t join certain clubs that I would’ve liked to.
Freshman: JV cross country and winter track, varsity spring track, boys scholar athlete leadership club, math tutor (unpaid)

Sophomore: same thing but all seasons varsity

Junior: office position for math team and science Olympiad, president of Math honor society, treasurer of science honor society, brainstormers club, history and national honor society member plus all activities from the previous years.

I feel pretty confident about my extracurriculars for junior year but I hope it doesn’t seem bad that I wasn’t committed to it for my whole time in high school.

Don’t worry about things you can’t change. Many HS students add activities as they move on in their HS career. The idea of the college application is to present who you are and what you have done in the best light so go ahead and do just that.