If you are happy with the percentile then you have no need to sit for the exam again. Now if you want to improve your score then you should go for the next examinations.

Now the 98.6 percentile implies that you have a predictive rank of around 14322 - 16100. With such rank you can expect any NIT's to get admitted in. So NIT's is not your problem but the branch you want to pursue in can be a issue. You will get CSE in most of the new NIT's thats sure. You can get old NIT's like Durgapur for CSE. For NIT Trichy & Warangal you have less chances for CSE but for all the else stream you have good possibilities.

Now to have more accurate prediction you can use the college predictor:

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

I hope my answer helps. All the very best for your future endeavors!