So you want to study science in high school, but crack the UPSC CSE, it will be 'harder' this way than if you had chosen to study Arts or History, which is an essential part of the syllabus of the exam you're looking to crack open someday.

But it can be done. I'd suggest you focus on your school, but take out an hour or two daily and start studying. Initially, don't sweat about how much you're learning. Try and get the feel of subjects like history, Civics, etc. Then if you like the space, you'll start reading more without effort. This will lead you towards glory.

I will advice you to go through arts because it's too difficult to crack upsc .n if you are open category then  it's a bit difficult. But it is wiser to go through arts of you have fixed to give competitive exams .