First and foremost believe in yourself .
Now let me tell u getting 90% is not that tough if you are ready to work hard to get and if you really want it .
Physics and mathematics both the subjects need your time as the best way to score in them is practicing questions from different books .
Only 18 marks are given to numericals in physics rest 52 marks are derivations so first understand and then learn the derivations this way you even if you forget things during exams you will be able to make out things logically . And for numericals one question will be from ray/wave optics , one from electricity , one from capacitance , one from either AC or magnetism and one from modern physics and trust me no numerical will be difficult for you if you just read ncert once and do all the examples and questions in between .
For maths the only way to score is practice you can give less time to the chapters you know and more to the chapters you are weak in but you need to practice . And do 1st chapter in the end because many people forget things about it if you start with it . And most importantly never be disappointed if you couldn't revise the paper in exam hall because it's almost impossible to take out time to revise mathematics paper .
For chemistry you just need to read ncert 2-3 times and I ensure you that you will score 90+ in chemistry .
Hope I helped .
All the best for your exams.

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