Assuming that your cohort's performance is similar to average past cohort performance, your rank likely means that you are on track with an Assessment Mark in the band 5 range. If that ends up being the case, an overall HSC mark in the band 6 range may be possible, provided that you achieve an Examination Mark that is sufficiently high that the average of both marks would produce an overall HSC mark in the band 6 range. Here, the higher your Assessment Mark ends up being, the greater your chances of achieving an overall HSC mark in the band 6 range for the subject if you also perform favourably in the subject's HSC exam. Additionally, a higher Assessment Mark means that you can get a slightly lower Examination Mark and still achieve a band 6 overall.
Let us consider some examples. Suppose that your rank in the subject leads to an Assessment Mark of 85. In this case, achieving a band 6 overall would require an Examination Mark of 95, as follows:
On the other hand, if your rank translates into a higher Assessment Mark within the band 5 range, such as 88, you would instead only need an Examination Mark of 92, as follows:
Of course, you will not know your Assessment Mark until you receive your HSC results. Because of this, it is important to do your utmost in preparation for the subject's HSC exam, so that you can perform at the highest standard and consequently have the best chance of achieving a band 6 overall.
I hope this helps!