Yeah I was expected extension to be harder and more relevant to what is being taught in math advanced.
I also do some science subjects. May I ask how you studied for the exams?
I studied the content in-depth, not just what the textbook teaches (surface level). Physics tutoring helped with this, but for biology I did my own research and used other notes I found, as well as asked my class group chat heaps of questions. I usually printed the syllabus and highlighted all the dot points I fully knew and read my notes while going through the dot points. This was most of what I did for trials as I usually crammed and it worked as I think I had pretty good exam technique so fully memorising + understanding the content was enough. For HSC (and sometimes for trials) I gave my bio teacher papers to mark, as well as peer marked biology papers with friends. For physics, tutoring helped but it was basically just past papers.
And as usual for every subject, try think of how to improve and reflect on each past paper rather than marking it and going like "okay nice 80/100 time for the next paper" like most people do since they think quantity > quality. For example you lost 5 marks using wrong units, then make it a habit next exam to highlight every single unit in the question so you don't forget to convert.