oh, dont lose your hope. I know someone who came back from overseas in year 10 and went into selective high school in year 11.
your school reports from usa and extra curricular might be relevant, so put them in.
I was going to suggest Vic selective school sample papers, but just googled them and they all changed now and not many questions...
I haven't use this but you might be able to get some sample questions from
https://www.notesedu.com.au/
and try both sample from HSAT and Edutest to which one you perform better at.