Please suggest how to get rank below 100 in IIt 2015. I am in class 12 . I have completed the jee syllabus. I have completed from followong books

Physics – HCV, DC pandey , Deb Mukherjee, Bansal and FIITJEE materials.

Chemisrty- Physical- Bahadur. Inorganic- VK Goyal (SHri balaji) Organic – Himanshu Pandey and Ms chauhan.

Mathematics- KC sinha and Bansal and FIITJEE

..

I still don’t have confidence whether i will get a good rank or not and also i wasn’t able to perform well in KVPY this year.

Please advice

If you are able to solve all the materials mentioned all by yourself, you need not worry about concept understanding. Better to switch to more numerical and question banks.
Also, KVPY and JEE have a very different approach of testing students. Not performing well in KVPY doesnot mean the JEE is going to be the same.

And from what you have mentioned about the materials that you have finished till now, you have come a long way. Losing heart won’t help. Concentrate on the study materials. Attempt as many test series as you can to better evaluate yourself and learn from your mistakes at these practice tests rather than the JEE.
All the best.