Hello Mahesh,
Inorder to get in the range of 200+ in JEE mains you need to be very concentrative on your strategies which you are following for your preparation ;

• Like if you have completed the NCERT then go with the other reference book for every subject.
• After the completion of your syllabus try to do the various mock test and test series for your confidence and to know the concept of every subject thoroughly.
• See, if you are preparing it from now then you need to leave those topics from which JEE rarely ask the question and try to focus on those topics where the chances of getting questions are more.
• And after the completion of your topic try to do the previous 10 years IIT-JEE paper which will help you a lot to understand the whole scenario.
• Believe yourself rather than your luck.
• Solve the past papers and solve them under time constraints while using a stop watch. This will amp your time-management skills which are very important for solving a paper like JEE Mains. Try to solve at least one whole question paper every day.
• When you solve question papers, look at the answers you got wrong and check for the theory behind them. Although it is advised to not learn new topics at this point, still checking the wrong answers will help you leave behind some memory of it in case a similar question appears in the exams.

I hope my answer would have enlightened you on your question.
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Respected sir,

For the last week, there are a few things you need to keep in mind 

1. Don't panic. Keep telling yourself that panic won't help and try to keep yourself as calm as possible.

2. STOP studying new chapters completely. It will NOT help at this moment. Revise the basic concepts and formulas, especially for the areas that are your strongest (yes strongest, not weakest). Make sure you get everything right in these.

3. Try some practice tests. A lot of them are available online with solutions. You could try the previous year Question papers or other sample papers at this time. The purpose is to put yourself through the 3 hour exam routine (preferably from 9:30 to 12:30) multiple times so that you feel comfortable on the day of the exam. (This routine is very important and neglected a lot.) Practice at least  3-5 (it would be ideal though if you get 6-8) tests before exam.