Hello,dear

First stay calm and instead of focusing on how,why these all just start studying , go to previous year question paper and start solving ,atleast 50% questions are always from that or any sample paper , now i don't know from which board you are studying and exams dates, but I will suggest you to solve sample paper question, and don't take pressure or think about how much time left just focus on study and be motivated always.all the best 

Hope this will help you!!