Work hard. I don’t know specifically but I’m sure maths will be important alongside your physics. Read lots – ask questions. Can you visit a big telescope or a planetarium? Keep an eye on other zones in I’m a scientist. They might have an astrophysics one and even if your teacher doesn’t sign up for a chat, you can read how the scientists answer the posted questions.
Obviously, you need to keep going to school and do well in maths and physics classes! Within astrophysics there are many different jobs you can get, so perhaps see if you can contact someone to arrange work experience or something to get more of an idea of what jobs are possible? But I know it is sometimes tricky to find good work experience placements.
Outside of school, there are a few things interesting things I can suggest you to that may enjoy:
Zooniverse is an amazing website! When scientists have a lot of data that all needs looking at, they can put it on zooniverse and anyone can help. You can start contributing to active research projects already! There are often many astro related projects on there. For example, this recent one about baby galaxies: https://www.zooniverse.org/projects/hughdickinson/galaxy-nurseries
TED talks are interesting (in general, not just for science). For example, you might enjoy this one: