Ask the school for the marks you got on the different papers.
If you are only 1 mark off the next grade, you are far from the boundary below and v unlikely to go down. You can go for a priority remark without worry really.
It would ask your parents to contact the Head of Year and say that you really need their help and support. It is bad if them to refuse.
Tbh, if it’s just 1 mark, I’d just go for it…but you need to know which paper - only do 1 or you risk one going up and another down and cancelling out a gain.