Hello there!

Greetings!

You don't need to worry,  just don't give up , keep studying and your marks will improve soon , you should not focus on only reading books , you should focus on how to present your answer in exam to get good marks,  you should focus more on the kind of questions that come in the exam and focus on important section from where questions are asked in the exam , you can take the help of your teacher for this.  These things will help you a lot , also try to grasp the concepts rather than learning them , and as soon as you start doing it your marks will start improving as if your concepts are clear you can face any question.

Thankyou