Around the end of last year, I said you could do it.
But after going through the Maths (Advanced) and Maths Extension books over the last 3 years, I say it's very hard to catch up. It's not a subject that can be covered wholly in a short 6 week course, this is a subject that is learnt over a long time 2-3 years on top of the university years.
For eg I look at a UNSW 2nd year Civil Engineering maths unit, this is its description:
"Partial differentiation and applications, vector algebra, double integrals, ordinary differential equations, introduction to vector field theory, extrema of functions of 2 variables, matrices and their applications, Laplace transforms, Fourier series, partial differential equations and their solution for selected physical problems."
a 6 week summer bridging course won't cover 1st year calculus (think it makes up 50% of the content in the HSC maths units) and vectors (if you take IB SL/HL- which I think is the hardest topic in SL). You would probably need to get a tutor or take possible a year long program to cover the basics.