Thank you for your post and for reaching out- I'm sorry to hear you are having a tough time with this. While I'm not on the LGBTQ+ spectrum I do know what it's like to have a religious family and have seen conversations like this go both ways. I want more than anything for your parents to be accepting and I hope that they will- although I hope that if they aren't accepting at first, that they will over time.
I'm not sure if you've heard but there's an organisation called QLife that offers free counselling and webchat. They could be a cool place to talk too- and it's all anonymous. www.qlife.org.au
Also, with your school counsellor they will need to abide by confidentiality, which means that nothing leaves that room unless you are at risk of hurting yourself, someone else or child abuse. Otherwise it's free range - which means you can have these conversations without your parents knowing. Please bug your counsellor about this, or even get him to clarify what he would and wouldn't tell your parents.
I hope this helps. There's a lovely bunch of people here who will no doubt offer some more support and personal experience