At this point of time, you should not ask which are important chapters instead you should ask the difficulty level of all chapters and how much time you should devote to the chapters.
For example if we consider chemistry -:
Chapters like polymers, biomolecules, environmental chemistry are not much important for JEE mains but they are scoring because usually one question is asked from these chapters which you can attempt if you have gone through the chapters thoroughly.
In physics -: electromagnetic waves is very small part and similarly logic gates part too but they also carry one question sometimes but yes with even less time devotion, you can attempt those questions.
So your strategy should be like this. See how many questions are asked from various chapters and prepare accordingly. Like in physics, many questions are asked from rotational motion, so you must be very clear with this chapter even if you have to give one month to this chapter.
You have enough time and try to give your best instead of thinking about these things.