What happens if I don't get all my math credits in highschool?

I'm seriously illiterate in math, due to never being taught math in a younger age, see my dad was never around and my mom would sleep all the time, (drugs, aha.) I never had anyone to teach me the basic math, so numbers just look completely messy to me. I know my basic adding and subtracting, but definitely not division and multiplication. I'm going to be going into 9th grade this year in September, and my grandmother (who I've been living with since I was around 7,) says that I need math credits or I can never graduate highschool. I know for a fact that I can't get these credits, because math is so incredibly hard for me. Every other subject though, I can pass with ease. Usually scoring an A, B, or C. Math though, was always an F. So, what happens if I can't get the math credits I need? Will I be held back in 9th grade until I somehow miraculously can get the credits? Would they hold me back for failing one class? Any answers would be greatly appreciated. Also, I'm not going to college, that would be impossible for me and my lack of intelligence. Some people just weren't meant for college, so, don't judge.