To be honest, just my opinion.
They won't really go mad at you for getting a Grade C/B in Mathematics GCSE as long as you get every other grade above Grade A or at A*, and go along with your predicted grades. Any grades which are B will make you most likely rejected, due to your maths grades. Maths is one of the core subject, they emphasise and look depth into the results of the core subjects. Also, getting a B in Maths would be good, if you need any help in GCSE Mathematics at all, I'm more than happy to help you, I'm on like 9/10 hours a day
got the app on ipad lol. Also, exam board for Maths? If it's Edexcel A, I'll easily be able to push you to that grade B, just by giving you tips, if you put in the effort to work, listen to yourself more than the tutor or anyone else. Your family, tutors, teachers, friends are all just boosts to your confidence or motivators, the true spirit is inside yourself, if you bring that out, no one can stop you from getting a D to an A*, and I mean it, just hard work, smart work and effort.