How to independantly introuduce myself into computer science?

I am currently a year 10 student, and since it is almost the end of the school year I will probably not be allowed to switch any of my options to computer science since I've probably already missed too much content, however since I want to work in the astrophysics/astronomy field once I'm older, I was thinking of doing physics, maths and computer science as my 3 options for A levels. I wanted to see where or how I could introduce myself to computer science so it doesn't hit me as hard in y12 or even to see if computer science is the way for me.

You don't necessarily need to have done it at GCSE to do well in the A'level. I would recommend looking over some of the GCSE content. Craig'n'Dave and Bitesize seem good.