You get BAD Chemistry test result because
you take too much time to learn chemistry.
You learn chemistry at home, doing home works. You understand the lesson, and you know how to answer home work questions, but you do not have enough time to study all the materials. And the teacher keep piling up new topics to study.
My solutions for you :
Drop Chemistry subject.
Make a summary of Chem topic
instead of learning the details of the lesson the first time. There is a better way to study rather than memorising the notes. You need to modify mind mapping technique to suit A level Chemistry.