Not every chapter is worth mastering. The gaokao has a fixed number of points and some of them are five-hour problems worth two marks.
Before spending another week on a topic you keep failing, compute the ratio: how many points does this topic represent on the exam, and how many hours would getting good at it take you? If the answer is 'four points and thirty hours', bank the four and move on.
This is not the same as giving up. It is deciding that your time is finite and there is a physics chapter next door where the same thirty hours might buy you fifteen points.
The rule works in both directions: sometimes a small topic you have written off is worth revisiting because you finally have the base to understand it.