If my kid got a B- even though they had got better before I wouldn't yell at them! I might ask some questions on why they found that particular assignment more difficult.

I suggest you find a therapist to speak to as it sounds like you and your mum (if you don't mind me saying) are putting you under a lot of pressure.

Be proud of your B- its a pass after all, I bet you are a bit of a perfectionist? I think some form of talking therapy would help you off load.

Take Care and do something kind for yourself today, even if its a small thing.