Hello,

To score good marks in Chemistry, you need to clear your concepts. I would suggest you to refer to the NCERT text books as they are the reliable source for building the basic concepts of all the topics. But, you also need to refer to other important books. Understand the topics well,  solve numerical questions, write important formulas in a separate notebook so that you can revise them regularly.
Solve previous year question paper, it will help you to know about the exam pattern and have an idea about the type of questions asked in the examination. Giving mock tests is also important. It will help in enhancing your speed and make a strategy to attempt questions in the exam.
Make a proper study plan and devote time to every subject to score good marks in the JEE Main exam.
Good Luck!

Sufficient practice from books like NCERt and OPtandon ar ehighky recommended, keeping short revision notes and group doubt solving is another effective way to score big. 

However jnless you appear for more than 15mocks you cannot get that level of confidence to scor ebig. Post which you shpukd analyze and rectify mistakes and focus in weak areas to score well.