What are the best topics to focus on ?
my teacher has been telling me that set songs carry most marks
Try to focus and practice the areas you feel you need to improve on.
With the music curriculum practice is the main way to improve!
Try giving some of the earlier year written a practice and see if your teacher will correct and give you advice where to improve!
The most marks are given for your practical followed by your composition and backing chords, the set songs aren't really your top priority