I just want to let you know that the HSC and Year 12 isn't the be all and end all of your professional life as so many stakeholders in schools make it out to be. When I was in Year 12, I got really depressed, flunked, and got less than a desirable ATAR than expected. Remember if things don't work out in Year 12, there are always other pathways in life, some people end up very successful in vocational education, some people work their way up to a university course through alternative pathways and entry programs, some people thrive by starting their own business, some thrive by entering the workforce straight away.
I knew people in high school that made it to uni and realise that make up artistry was their passion and dropped out, I also know people that started in floristry courses and realised that retail wasn't really for them so they pursued nursing instead.
My advice is to do the best you can, and regardless of whether you felt you succeeded or not, know that there are many pathways to the future for all of us.