You have posted quite a number of very similar threads now regarding your 58% and Further Maths. I would encourage you to bump your existing post (and/or make amendments) rather than continuing to post threads that relate to the same issue. Don't worry now, but for future reference.
Now, in terms of your question, your actual numerical/grade achievements in Further Maths are (in a way) irrelevant, because all that matters is your rank. SACs contribute 34% to the study score, and the two exams cover the rest. So in theory, what study score you get is entirely dependent on your SAC rank and your exam performance.
If you get A+'s on both exams, I think you'd float somewhere around the 40s range depending on your performance relative to the others who received an A+. You have to remember that Further is extremely competitive, so the goal is to minimise mark loss in both exams.