Be a good student.
Be patient.
Do not jump ahead too quickly. You are already for example way, way ahead in math. It is important in math to learn each step very solidly before you move on to the next step.
In terms of ECs, do what is right for you. Whatever you do, do it well. Be genuine. If you get into a leadership role, then listen, and make an effort to make the activity better for everyone. Leadership is not about being the boss. Leadership is about helping people and being responsible (and yes I do wish more voters would keep this in mind).
Understand that you are already doing very well. You do not need to do anything special or flashy or extraordinary. Just be a good person and be a good student and it will work out in the end.
And one A- will not matter. One or two B’s won’t matter either if these occur at some point.
Given that you are way, way ahead in biology and chemistry, I will give an additional piece of advice in case you ever think that you are a premed student: You will be a stronger student in four or five years than you are currently. Many of the required premed classes are really, really tough. The competition in these classes will be very, very strong. You should not rush to take these as early as possible. Instead take them when you are very ready, which is likely to be in your second, third, and fourth years OF UNIVERSITY.