Greetings!

Let's get straight to the point, First I would point out, that you are still in better position than many of the aspirants, because at least you know have not studied anything and you are ready to work on it, there are lakhs who don't even know that.

So first step is to stop panicking and start the planning.

The first advice I would like to give is the exact quotation from my class 11th teacher- "The first step to clear back log is to stop it from piling up". i.e the first thing you need to do is not to go and study old things, no the first thing must be to focus on current topics...

Now let's go chapter wise- In physics you have entire electrodynamics and modern physics left. Now if you study electrodynamics, the gravitation will automatically become clear, and after that your target must be 2D motion, NLM, work power and energy. With these topics in your hand you can easily score 40-50+ in PHY alone

Coming to Chemistry- Now here I would say focus on physical chemistry that you are being taught, it is not much related to previous topics. Then for inorganic you have to mug up things and that is what will give you marks. Then just before organic starts go back to class 11 organic and study it properly, organic alone makes up roughly 40% of paper many times. So in conclusion study organic and inorganic properly, in physical you can cherry pick chapters you like with that you can get around 50 in Chem

Now in maths, again primary focus has to be calculus, that makes up the large portion of paper, and then pick topics like Mathematical logic, Mathematical induction  and statics. more often than not you will see 2 questions coming from such topics. Now after that move to Relation and Function, then if you have time go for P&C and probability

With this much you should be able to get 100+ although it does highly depend on how much practice you do on these topics

~Sach Thadani