well at unsw for first year, math1151/1251 (actuary) is far harder than math1141/1241 (advanced maths). but take note that actuarial studies is APPLIED STATISTICS and not neccessarily 'maths' as you would define it.
first year is a relatively easy course because a lot of it is just re-teaching aspects of the 3u and 4u course. second semester starts to introduce new concepts to you, especially in algebra. i did zero study all this year and pulled off a 70-odd (which is not impressive at all) in math1241 and your hsc maths marks are much better than what i managed in 05. someone like you should be able to get mid-80s and higher with some reasonable amount of work.