Maths (and F maths) are very honest A levels, put in more effort and practice and you will get higher grades.
Maths is rather straightforward, just start doing past papers (from multiple exam boards) asap, eg Christmas in year 1. This will help you understand the level you should be working at.
For F maths, the second year is a big step up and it's worth skimming over topics/pre learning to get a sense of how everything fits together. It's very easy to get over focussed on a particular technique and lose sight of the bigger picture.
Also, you need to do well in your third subject as well. Maths may be the easiest subject you take.