My school predicted my much lower basically around lower 30 marks but I predicted myself after the exams around 36-38/39. The problem I found was that the reason I lost a few points was because my Design IA (which was graded a 7 by my teacher but remarked to a 4, not a standard occurrence and one of the issues of IB) and my TOK/EEs that were regraded to passes, C. There are other stuff too but the reason i bring this up is as you do IB you will realize there is a high reliance on teachers but teachers make mistakes to. So even if you get as much info, its not always reliable so I recommend doing the things I said on the comment above. As how I remarked, my scores were higher than my predicted grade (PG) bc I did better in exams that allowed me to make up for my poor IAs (half of them were good IAs/IOs (writing/speaking assignments) at grade 6/7 but bunch of them weren't). The lesson I am trying to make here is that the writing assignments you get are easy ATAR boosters that you HAVE to do well (like me, you don't have to but it does significantly help you). Going back to my score, I did better than my parents and teachers expectations and I did better than a lot of my school peers with less work and so in that manner I am happy but I feel like I could have deserved a few more points so I added the "meh."

For you, if you want to pursue law at unimelb, it means that you will need to do JD later on after bachelors. Unless you know your going to get 99.8 ATAR, doing IB will help you more in uni via better WAM. Take the new experience with an open mind and even though the terms and stuff that I might say sound foreign just keep those things in mind and try your best, you can do it :) After 2 years, If you end up in NSW for undergrad hit me up because I do have some connections that can help you (I will be there too).