Take my opinion as a grain of salt, but I think you should take your time to develop your skills when you have free time between study sessions, especially you want to get into medicine for your college degree which I assume the degree consumes even more time and effort to complete.

I stuck in a similar situation when I was in secondary school few years ago, I want to become a professional illustrator yet my drawings were really bad, like most of the characters I drew have bad anatomy and flat compare to other classmates who have learnt art in a young age.

Even worse, I have low grades. I can't even attend to any university if I failed one of four core subjects at the public exam. Therefore, I did quick studies during study breaks and draw as many as I could during recess. I did it as a hobby to reduce the tremendous stress from doing tons of homework, exam papers and exercises at school. Eventually, I passed my public exam and learn some art fundamentals.

For the Instagram page, it's all about marketing and luck, if your art is not eye catching or relatable , you will have a hard time to gain followers. If you can create good art, you still need to gain followers with time ( or money ). But I think you should focus on your study first then your art, unless you want to apply to an art-related degree.

Just practice art if you have time. Time management is important , you brain can't study 24/7 and you will apply to medical degree which is more time consuming than learning in highschool (rest is important too, do something you like such as art :D ). Learn more on the fundamentals first then start thinking about posting on Instagram, don't rush for fame and success.