if I got one of I liked NIT , in first round , second time I got another , third time I got another , did I am able to take first one in last round?

Counselling is done as per candidate's choices and it goes from up to down. That means the system always check your 1st choice then 2nd then 3rd and so on. If you get your third choice in round one and select float, the system will try to give you your 2nd choice in round 2. If you get 2nd choice in 2nd round you will lose the third choice as you did not accept it in round 1. In this way if you get your first choice in round 3, you will lose your second choice too and you have to accept this choice and take admission in that college.

Hope you understand. All the best.