Kaif, NTA score of 66 refers to the percentile you obtained in the JEE Mains exam. It refers to your relative performance with respect to the other appearing candidate. That is, if you get X percentile, you performed better than X% of the total candidates.

So a score of 66 means that you did better than 66% of the total candidates who appeared in JEE Mains January session of 2020. Now you can calculate your approximate rank for JEE Mains using your percentile through the following formula:

(100-your total percentile) x 869010/100

So with 66 percentile, your rank would be around 295463.

Also, if the number of students increases to 12 lakh in the April session, the formula for rank calculation would change to:

(100-your total percentile) x 1200000/100

Hence your expected rank in this case would be around 408000.

While it is difficult to predict the exact qualifying cutoff, a percentile of 85 or above is decent enough to qualify for JEE Advanced for the unreserved students. In 2019, the NTA score cutoff for the Common Rank List was 89.7548849

According to your percentile, it will be difficult to clear the cutoffs for JEE Advanced. Also you won't be able to get a seat in the top NITs or IIITs with this rank. I would suggest you to sit for the April session and give your best in that exam so that your chance of qualifying JEE Mains and getting a top college increases. Solve the previous years' papers, brush up your concepts and revise thoroughly.

You can also go through our college predictor to check which colleges you are eligible for through your JEE Mains score. The link for the college predictor is:

All the best.