Short answer is yes, assuming you are the student in last place.
It depends on how you three go in the HSC exam. Your school marks are marks based on your school assessments. But you can't really compare your school marks to the marks I got in school because we sat different assessments, of potentially varying difficulty. So BOS uses the HSC exam as a measure of objectively assessing how a student goes at school. To do this, BOS considers the average of the school marks, the average of the HSC exam marks, and "moderates" or adjusts your school marks to reflect how you may have went, had your assessments been the same throughout the state and of HSC level difficulty.
Since you have 3 students in your class, it's easier to explain what BOS does. The student ranked first will receive the highest HSC exam mark of any student as their assessment mark. The student ranked last will receive the lowest HSC exam mark of any student as their assessment mark. Then the student ranked second will get a mark that proportionally reflects their position between first and last. If their school marks were closer to first, then their assessment mark will end up being closer to first. If their school marks were closer to last, then their assessment mark will be closer to last.
BOS also considers if they need to raise the mark of the last ranked student, if the average of the newly calculated marks don't match the average of the HSC exam marks. Basically, your assessment mark cannot be lower than the lowest HSC exam mark of you 3.
Now, in your situation, you are saying two students get 100 as their school mark, and third/last gets 60. So this situation means there's an equal first situation. The assessment mark of the two equal first students will be the average of the 2 highest HSC exam marks, but last will still get the lowest HSC exam mark of any student.
But in all cases, you keep your own HSC exam mark. If you get 95 for your HSC exam mark, you keep that. Your assessment mark will depend on the overall class performance and how the other 2 go.
BOS also considers the expected performances of individual students. If those 2 students who are getting 100% ends up getting a crap mark, that is much lower than expected, BOS has the ability to remove them from the calculations to ensure fairness of marks.
Essentially, you 3 need to help each other to do well collectively because if any one screws up, it has the potential to screw everyone's marks.