Probably better off doing Standard Maths if you are already struggling. Rather than ranking last for advanced maths, you would be most likely at the top of standard maths, and therefore would be better off. This is what most people do anyways back when i was in high school when going into year 12 after finishing year 11, about 20 people in my year dropped from advanced to standard because they werent performing well. One of my other friends was on a B4 for advanced but dropped to standard just before trials in year 12 and ended up getting a B6 for it.
Not sure if your school does it, but back when i was in year 10 after the first semester, the school gave us recommendations on what subjects to chose based on semester 1 report results. Maybe take into consideration what your teachers recommend when making your final decision. If you do end up doing advanced maths anyways, you can always drop it after year 11 anyways like my friends did. The work is much easier, and wont be a problem catching up on year 11 work if you are worried about the work being different.