Keep up the good school work. It's vital that you build a strong foundation for the sciences, a desire to never stop learning. Mathematics — It'll open doors and give you options just like you originally planned. But never forget about others; people are important, each interaction moulds us.
Take risks. Ask for more. Feel rejection early on. You'll come to a point in which you will fail. School is a microcosm, a finite game in an infinite one. Yes, the lessons learned and grades obtained will decide the paths you can take. However, it isn't the be-all and end-all. You know this already.
I think about if you should take this on board, whether to explore more outside school. Make things whilst you're young. Write. Draw. Create. Be aware of failure but don't shy away from it. Calculated, not dismissive and wholly, risk averse.
...
Writing to my younger self. If, somehow you we're able to read my advice, what would become of me today?
It reminds me of Ted Chiang's shorts, Story of Your Life and the Merchant and the Alchemist's gate, both exploring the nature of time. How, in the first story the narrator learns to perceive time not in a linear, sequential order but as "a refracted ray of light must know all possible paths to travel along the minimal path".
And in the second,
Past and future are the same, and we cannot change either, only know them more fully.
...
Future me,
Pay attention to what has been said to younger us. I trust you. I trust in the foundation our younger self has laid. I trust in the decisions we make, whatever the outcome.
What's the point of hindsight?
I, writing this, currently believe there's only one thing I regret so far. If one can learn from their supposed mistake, then I would like to think regret doesn't fit. There's still time, only now you know what it feels to lose. In all seriousness. I hope whatever you're doing, wherever you are, that you have stuck to our values.
Your nails better be pristine :)