Dont worry Priyanshu, it will be okay. Just keep calm. I know u have done whatever you could. It happens sometimes. Just leave, u cant do anything about it now. Focus on other subjects if ur exams are still going on. Dont let this paper affects your other exams. Best of luck. Hope for your beat.u have tried your best and u will continue to, i know.

Well, You must Look Forward to do better in other subjects. Well it was my personal experience of 12th board where i was not much happy with my physics paper, but still i had to score a good percentage , so i concentrated on other subjects. This way u can compensate the lose which u made in physics and can increase ur overall percentage. In my Next 3 exams I scored 65, 65 , & 64 out of 70. So that helped to get 89% in 12th board.

Make a good look on the  derivation which will be asked for huge marks comparatively.And also note  the small and simple definition that can be easily catched. I think you should concentrate on the 2nd part book.
Good luck for the exam.
All the best