You go to a strong school accelerating a subject so lets assume (quite conservatively I imagine) that the top exam mark is 96. You are ROUGHLY 10% behind the rank 1, so if 96 was the top mark lets assume you get around 86 as your internal mark. Seeing as the hsc rounds up, you would need to get a 93 in the exam ( (93 + 86)/2 = 89.5 which rounds to 90) to get a band 6. Thats what I can see happening. Given I dont know a whole lot about how good you or your cohort is, or even how your school submitted their assessment marks, I think if you work really hard and get a good external mark you can get a band 6.