You're going to get 90 for exam mark.
For assessment mark, you will get the 32nd highest mark in your class. BUT BUT BUT that mark is not necessarily the 32nd highest exam mark achieved by your cohort. To work out assessment mark, they take the highest exam mark (regardless of their rank), the lowest exam mark (regardless of their rank) and position everyone depending on the gap between their internal assessment between the top and bottom.
For example, if you get internal mark of 55%, first gets internal mark of 75%, and bottom gets a mark of 25%, and if the highest exam mark is 90, lowest exam mark is 80, you'll get an assessment mark 86.
If I've made an error, somebody correct me (but I'm fairly sure I haven't). If OP doesn't understand this, just trust that it'll be graded fairly (i was like you, bad rank with good HSC mark, all turned out good and fair).