Bad economics teacher

in year 12 i used to have a really good teacher for econ, she taught well and i was able to get a A* for econ but she left and we have this really awful new teacher she cant teach or even mark properly for example she forgot to mark one of my questions. Now i get B's Even thought i now ive got at least a A for my tests and its affected my predicted.

Any advice on how i can get a A* by myself for my actually econ exam because at this point i would be better of without a econ teacher