Sir right now I am final year student and I got 45% in my 2nd year and before result I fill up my cat form expecting 50% in 2nd year.

Even if your application has been submitted and you get your admit card you shall not be accepted for admission as you won't be eligible.
I understand that you are getting good percentile in mocks and you should continue with difficult level of questions and sums and keep the practice continued but at the same time even if you score good in the exam you will deselected.

You can give the exam for your practice and then appear next year with full confidence and practice.

If you are asking that you have less percentage in your second year and you have filled 50% and not 45% then it can be a problem at the time of admission because the minimum percentage of a candidate has to be 50% for first and second year in total and not just second year percentage you have to mention. This is the case when you are in your final year and your results re awaited.

So a correction window is expected and then if they allow you can edit the percentage for aggregate of first and second year.
Good Luck.