You have a pretty good academic records so you don't need to worry about that. You should know that every IIM after CAT exam makes a merit list based on your aggregate score which comprises of many factors such as CAT marks, 10th 12th and graduation percentage, work experience, engineer or non engineer, gender with different weightages for different IIMs. Among which your graduation percentage weightage is around 10% in your first merit list whereas CAT percentile has highest weightage of 35-60% in almost all IIMs.

To get calls from top 3 IIMs i.e. IIM A, B and C you need to score above 99.7+ percentile. IIM B has a little different criteria along with it as it gives way more weightage to work experience. For other old IIMs like IIM L, K and I you need to score above 98+ percentile. I will recommend you to target to have above 99+ percentile in order to have a high probability of converting your call. Again here IIM I has a little different criteria as it gives way more weightage to academic records even more than CAT marks.To get calls from all new IIMs you need to score atleast above 95+ percentile.

Always aim for a high percentile and you will cover up the small loss which you have due to your graduation percentage. But believe me don't worry about it and focus on CAT exam i.e. about to come. Give lots of online mock test and analyse their solutions which will help you in overcoming your mistakes and making up a strategy to attempt the paper which will definitely help you in improving your marks and percentile.

All the best for your preparations and exams!!

You have decent past academics and your chances to get in old IIM's based on your scores is average. It is not that you can't get admission in the old IIM's. There are other judging criterias as well like GD/PI/WAT and mainly the entrance exam.

70% weight age is given to CAT exam so don't you worry about your past academics. BUT because the competition is high to get a seat in old IIMs aim at getting a percentile near 99.8 to get admission in the ones you desire. This may sound big but thats the number to get.

Also the selection criteria may vary in all IIM's and just to give to an idea for the same I am sharing a link which states the detailed selection process for IIMs.

IIM's Admission Criteria

 

All the best!