I got 48% aggregate in my first and second year. I am final year student and I will be pass out on may 2018.

Hy riya,
You are from general category so one thing you need to keep in mind that if you fail to get 50% at the end of your final year then i am afraid to tell you that you won't be able to write for cat 2018.

Eligibility for cat

The candidate must have completed his/her graduation (bachelors degree) or passed an equivalent qualifying examination from a recognized college or university.

He/she should have scoredminimum 50% marks (45% for SC/ST/PWD). The bachelors degree must be ofminimum 3 years duration.

CS/CA/ICWA candidates and candidates who are in their final year of college are also eligible to apply.

So kindly focus on your last year first at it is very important for you to score atleast 50%  somehow to be able to give cat.
I hope you will get it by the end of your last year.
I wish you all the best.
Don't loose hope.
Cheers !!

First of all you need to make sure that your graduation score goes above 50% by the end of your final year otherwise you won't be even eligible for sitting in CAT exam. You need to have above 50% marks in 10th 12th and graduation all the 3 academic areas.

You should know that after CAT exam every IIM 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 colleges.

With poor academic records you have a huge disadvantage  in your aggregate score as it covers around 10-25% in your aggregate score which could be a little covered by you as you are a commerce students so you will get a little edge on fellow students who are going to appear in the CAT exam with you because you will get extra marks for being a non engineer in your aggregate score. Also looking from previous records a non engineer gets a call from IIMs at a little lower percentile than the student of same category.

To cover your rest of the loss and to ensure your call from top IIMs you need to aim for a very high percentile. Scoring above 99+percentile  can definitely get calls from most of the IIMs. Work hard and prepare well for CAT exam With an aim for a very high percentile.

All the best!!