You can transfer to engineering or computer, and have a certain related foundation. Of course, the sooner you prepare, the better. Now you can find a major, so pay more attention at ordinary times.

However, theoretical physics is not without money. Keep your brain alive. You usually think of something of practical value, not necessarily astrophysics. Think with relevant knowledge, and then you can contact relevant enterprises and earn a lot of extra money. When it comes to making money, physics is a chicken that lays golden eggs.