Bit hard to find a really good dark sky around the Sydney area. You would either have to go a fair way south or south-west. And I mean a hundred klicks or more. It's been a while since I lived in Sydney. How far are you able to get your folks to drive you?
South you've got the "Gong" and North you've got Gosphord and Wyong.
Maybe sonewhere about the middle between Helensburg and Bonnie Vale, might be Ok but you really need maybe to head for the sticks around Burragorang. Mind you that's a fair drive from where you are. Got any school holidays coming up
maybe ask your folks for a weekend away down between Ulladulla and Batemans Bay or even further south. Or maybe go for a holiday drive out towards Orange, but further south..