I don't know in which examination you have qualified for the examination. Now in general the discrepancy in the provided details is taken as an serious disciplinary measures for most of the colleges. Now if you have made this mistake then you have to contact the IIT KGP admission cell as soon as possible and get it discussed.

Now in general it will not led you to serious problem as most of the examinations the asked CGPA is around 6.0.So you will cross the eligibility thats for sure. So don't worry just inform them and they will guide you some ways to change the information.

I hope this answer helps. All the very best for your future endeavors!