If you want to enter a physics major you definitely need a very good math basis. Searching across the internet I found Khan Academy (https://www.khanacademy.org/) Especially focus on the trigonometry and precalc courses.
If you want a more serious focus to math, start by checking two books I use on college: Calculus by purcell and apostol vol. I (Purcell: http://libgen.io/book/index.php?md5=849F5D61A7DC22EECCCACBF805CB4891) (Apostol vol I: http://libgen.io/book/index.php?md5=A4EEEE29CE4849B2777C7D53806945C8)
Physics knowledge may even be secondary if you have a good calculus basis. Check them out.
Don't lose this opportunity! Good luck!
Btw, when I started I was also deep into astrophysics, but now I've realized my true love is theoretical, so don't prejudge yourself by thinking what you like may be wrong or stuff like that, physics is a whole new world, explore it!