I know the maths grade boundaries are very high.
Remember however that if you got the answer right in a question that you will receive full marks on that question.
Again, examiners are very lenient on maths papers due to its linearity so it's understandable if there are things going wrong here and there.
My A* boundary in my exam was only 1 mark less than 170 and I was surprised that I was far into the boundary even though I thought I got more than 6 or 8 questions wrong.
Don't worry.
All will be well, for sure.