Actually when I was applying for CAT at that time my part 2 result were not declared so I entered 55% aggregate of 1&2 year.

No there won't be any problem. After the CAT exam in the first list i.e. calling you for interview, you will be evaluated on 55% only. Then when you get a call for interview each college individually ask you to fill up your details again along with some other general HR questions. These details are used during the interview.

So while filling these details you can change your percentage to 60% and then verify it with your marksheet when all documents are thoroughly checked on the day of Interview. Then your this percentage which is better than last time will be used to make up your aggregate score in the final.list of selection.

There won't be any problem. Even during my IIM Kozhikode I got my percentage edited becuase while filling details I made a mistake in converting CGPA into percentage. Without any problem change was done and I got selected in IIM Kozhikode where I am currently studying in 2nd year.

So don't worry and prepare well for your exam.
All the best!!