That anxiety is quite normal - that’s always going to be the possibility for a time constrained exam with questions that sample the problem solving skills across a wide population of students, but if you’ve been able to solve all the questions in the past papers and trials, then the wide sampling suggests you know the syllabus well enough to achieve a good mark. There’s an element of luck to achieving a state rank as the discriminatory question(s) can be on almost anything in the syllabus.
If you do encounter a question that seems unfamiliar, keep moving on through the paper and come back to it after you’ve finished solving the other questions. Sometimes, the relief, after completing the rest of the paper, clears the mind so that ideas can better flow on how to approach difficult solutions.
Best wishes!