Hello, dear

Don't worry stay calm and be positive, I would suggest befor that I just tell stop thinking how will you do that you just instead of how just start doing .

Well now you have as well your board exam if you are from cbse , so just revise from notes and which ever subject you like more you focus on that try to get in command of your favourite topic , if i would talk subject wise

In maths few chapters are very simple , like matrices ,vector , probability as well these are small chapters you can study it easily !

And in chemistry ,go through notes you will definitely score ,study full note if you don't take help from any friend ,

And phyics topics need concept so you have to give some time ,study optic once you get how to solve optics you will see ,you will find it easy and thermodynamics as well these two are most important. And just be positive you can do everything.

All the best