Exam

Your JEE score is decent for top colleges. Check the colleges through this link:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

According to the data, 2.5 lakh students are nearly selected for JEE Advance 2019 but I think, nearly 1.7 lakh will give JEE Advance exam because of the matching date with other exams like WBJEE, etc. Also, JEE Advance is quite tougher as compared to other papers.

For DU entrance exam, I would recommend you to go through Bachelor of Economics honours syllabus of Delhi University. It will help you a lot and for JNU, I am not very sure but I think the syllabus is almost the same because many of the students from Delhi University who have done their Bachelor's degree from Delhi University go to JNU.

Yes, you will get a seat in Shiv Nadar University with this score. Last year, students with the same score got a seat in the same college.

Yes, you can get admission in Amrita University. Your rank is good enough to get you a seat in this college. You can apply with your category also to get reservations benefits. And keep all the documents ready for verification at the time of admission.
Best of luck.

You can see your score on the website of NTA:
https://jeemain.nic.in/jeemainresult/Root/AuthCandWithDob.aspx

If you belong to the general category then with this percentage forget about any scholarship or a concession for a branch like CS.

JEE results are out, check it. IIIT-Hyderabad, VIT-Vellore and other private colleges will announce the cut-off rank after JEE Advanced exam is over.
All the best.

For the computer science branch, it would be around 90% to be at the safer side. For more details, you can click on the link given below:
https://www.shiksha.com/college/pune-institute-of-computer-technology-society-for-computer-technology-and-research-pune-satara-road-3715/admission