Nikhil Congrats on a good score!!

For your Agricultural branch with your 641 marks yes you have a good chance of getting admission in IIT Kharagpur. 

There are 2 subjects available in IIT Kharagpur related to Agricultural engineering - Agricultural Biotechnology and Agricultural systems and Management.

Among these 2 seeing the last 3-year cut-offs you can opt Agricultural Systems and Management as both Major and Minor because it's cut-off for both Major and Minor has always been below 600 marks whereas you can opt Agricultural Biotechnology only as a minor course because for MAjor it's cut-off has consistently crossed 700 marks.

The first step for admission at IITs is to apply to the IITs individually through their respective application portals. In the second step, the candidate will have to get registered on COAP to be able to check the status of admission offers and to make a decision against those offers.

All the best!!