im currently doing hsc adv and imo you can def catch up over the holidays. here is smth i said to someone else else that wants to catch up for maths. you can use textbooks/past papers borrowed from school or whatever and whatever you can find online on thsc
go through examples/info at the start of each chapter if its useful and if you think you got it just skip to end of the chapter and grind out the chapter review or the harder q's in the exercise. if you're worried abt skipping important content by skipping through the textbook just look over a few of the other q's and try it with no working to see if it makes sense before going to the harder q's. this should save you a majority of your time as opposed to smashing out the entire textbook
and then grind through practise papers. prac papers are more important than textbook so make sure you get through the textbook quickly and move on to prac papers or q's. you got this!
if you have fallen behind i seriously don't recommend going to a major tutoring place like dr du and stuff bc they are often well ahead of the syllabus (currently doing y12 content already) and will only confuse you more. id suggest looking for private tutoring or one on one tutoring, there is usually always someone that is local. prices can be a bit insane but if you look for uni students and stuff they usually would have done well in the hsc as of recently they charge more reasonable prices
hope that helped! you can ask me if you have any questions
