As a junior, what are the biggest ways I can improve my admissions choices?

I agree with @facilityburton; increase involvement in ECs and study for SAT. However, you are already doing VERY well in PSAT and will likely do awesome at the SAT.

Also, start thinking about college essays. It's not too early to start brainstorming ideas and creating structure. I wrote an extensive post about college essays you may find helpful: collegevine.com/c/junior/49537/make-your-essay-stand-out

As far as ECs, increasing your involvement would be beneficial BUT maintain a balance- you need time to rest, eat, and breathe! Don't scramble around trying to pick up as many ECs as you can; instead, find ways to explore your interests/hobbies further. Sometimes these things become our careers (mine are becoming for me!) and it's important to do things you enjoy.

If you have any other questions, lmk. Happy to help :)

Your extracurriculars are quite good. If you want to improve them, you can get deeper with them, maybe take higher leadership positions or participate in more competitions. As long as your ecs align with the things you're passionate about and you're able to bring out that passion to admission officers, you should be fine.

I would advise studying for the SAT even though most schools have gone test-optional because it's another advantage to have in your application. For your essays, you can start brainstorming different aspects of your identity (i.e race, culture, ethnicity) that shape who you are and jotting down the experiences you've had in your life that have influenced you so that when senior year comes, you wouldn't spend ages trying to wrack your brain to come up with something unique.

Dont be like me who is trying to rush supplemental essays, and hopelessly looking for who to review my essays before the Jan 1 and Jan 2 deadline. Learn from my mistakes and do better. You can do this :) !!