Recommend me math help.

[Thatskier]

So awhile back I made a thread on whether to take Calc AB or Calc BC first. So I decided to take the harder of the two, being BC.
Now seeing I just took two tests on chapter 3 (derivatives) not basic derivatives but every kind of derivative (at least that i know of all the rules and implicit differentiation) and i got a 55% and 60% on the tests. The problem is I understand all of the information. I'm not sure why i failed both tests but our teacher makes his own tests that he says are much harder than the AP exam on purpose so when we take the AP exam it is easy. But the chapters will get harder. I thought iv been studying and doing homework all good and dandy but apparently not. I think the multiple choice is killing me (no points if wrong answer). So... help? Khan academy is good and all but thats teaching concepts in a very slow manner that i already get.... :\