Anyone can learn this subject and if you find you don't excel in relation to your peers in pure cognitive or intellectual capacity, that's ok. You were probably never going to be Einstein anyways as that's just not what physics is like these days. There are 10,000 Einsteins out there picking at higher fruit and they do good work. If you wind up being one of them, great! If not, don't sweat it.

If you gruel it out and hate it and barely pass there are still many career paths for you to love and enjoy in space. If you want to work in PR for Space X, it sure helps if you understand why a satellite needs fuel to stay in orbit while you explain it to the press and that degree/knowledge is what enables you to do that.

Take me, I excelled pretty spectacularly academically but didn't have opportunities and do not have the degrees or depth of knowledge required to say, be a professor at Harvard but I am a 3D artist who has worked on things you've probably heard of.

So to your questions:

1. Don't be scared of hard, the mountain of knowledge required scares literally everyone
2. Take it one step at a time
3. My personal recommendation for people like you is whatever subject you're into with the most math or CS-skills. Astrophysics fits that bill, astronomy not so much. But you do you and there's 0 things wrong with a passionate pursuit of an astronomy degree.

Just relax. And play Kerbal Space Program for 1,000 hours before you take your first class, you'll thank me. Use YouTube tutorials for when you get stuck ;)