I dont know why you want to get into IIT Kgp as you are already studying inthe other best college i. e. Meshra. The ranking gap of these two college is just by 3 - 4 colleges. And i am pretty sure that you wont be getting a very good branch there either m.sc. in economics or applied goology. I should make you aware of the fact that its ot very easy to get your branch changed after the first year, just scoring good doesnot help. Branch to which you will be opting should have some students going for a department change. At your position I will prefer to stay at the same college and study well there.