JEE

If you are sure that you can do better next year or you can get some good college or a better rank in JEE, then you have to wait for it, otherwise don't waste your time and money.

Sorry to say but it is difficult to get admission in NITs for you.
Chances are very less. Apply for JOSSA and perhaps, you can get an admission by luck.

Check out the link below and click on the link below now college cut-off:
https://www.shiksha.com/b-tech/resources/jee-mains-cut-off-predictor

For engineering courses, JEE is the only exam to get into IITs.

You have a chance to get admission in NITS like NIT-Jaipur, Nagpur, Surat, Warangal, Durgapur, etc. for CSE.
Best of luck.

Drop is not necessary step for IITs. Many IITians haven't taken any step. If your focus on your goal is clear then you can also clear IIT JEE without drop.
Your concepts must be clear whether you take a drop or not.

In which state are you looking for?