What should you do if you got bad grades but don't want to change schools and don't want to repeat a year?

Hello!

I earned my intermediate school leaving certificate (Realschulabschluss) this summer, and since I was in the A-level course, I went to a community school after graduating. I'm currently in the upper secondary school (Gymnasium) and got a C in a chemistry test (yes, I studied, but neither chemistry nor physics is my thing, so I'm going to drop chemistry), and today I got a D+ in math.

I'm extremely worried that I'll have to repeat the test or change schools. My friend got a B and she also comes from a secondary school. I just don't understand math, and today I asked my mom if she could sign me up for tutoring. My friend, who got a B, also offered to study for the next math test (this was the first math test).

My worst grades so far were:

4+ in Biology

6 in Chemistry

5+ in math

I think I can improve in biology on my own, but I'm extremely worried about math and chemistry. I definitely don't want to change.

(I was bullied at my old school in 10th grade, people made fun of me, and these students who annoyed me a lot go to the school I would have to go to if I were to change schools)

But yes, any other tips on how I can get used to the upper secondary school or how I can start studying intensively?