B.Com

I am afraid that you cannot join Merchant Navy. Only the Science stream students are eligible for job in Merchant Navy. But since you have completed graduation in commerce, it closes all doors for you.
The candidate who has completed 12th standard with Physics, Chemistry and Maths is eligible for job. He can directly apply for deck cadet job after completing 12th or wait and continue with the studies.
Those who are interested in officer level jobs continue with the studies and pursue either Marine Engineering or Nautical Science course. Unfortunately, commerce students are not eligible.
Indian Navy recruits commerce graduates in Logistics Cadre under Short Service Commission and Permanent Commission both. You need to take an examination called CDS (Combined defense service examination) which is conducted by Union Public Service Commission twice in a year.

GCCBA, Kolkata is quite better than KIIT School of Management. Here are a few reasons:
1.GCCBA established in 1905 and KIIT School of management in 2003 so KIIT is new and GCCBA is old so obviously there are some good things in GCCBA that's why this college is running since a long time.
2.Fee Structure of KIIT University, School of Management is very high as compared to GCCBA Kolkata
3.GCCBA college is having all the world-class facilities for the betterment of the students and KIIT mainly focus on B.Tech.
4.GCCBA college is especially for commerce studies and KIIT gives a degree to almost all the course this mean GCCBA care about this and established especially for theses course and KIIT doesn't think much about these courses because this degree is minor.
GCCBA offers undergraduate and postgraduate courses with specialisation in commerce and business administration.
For more details about GCCBA-Kolkata, check the link provided:
https://www.shiksha.com/college/goenka-college-of-commerce-and-business-administration-gccba-kolkata-b-b-ganguly-street-13132

First, decide yourself what you want to do MBA or job, because if you are planning for a good college then I would rather suggest you to study for CAT exam with complete dedication of taking admission this year. CAT needs a lot of practice and study to get admission in good colleges. If you waste time in deciding these confusions you will not able to give CAT exam at good stage. So I would suggest start preparing for CAT entrance exam with complete dedication and Self-motivation. Then if you get a very good score go for TOP MBA colleges to complete your goal and if unfortunately you couldn't able to crack CAT exam then you can go for any suitable job for one year then you will have time and you can prepare will for next CAT exam.
While doing your final year you will have a flow of study for CAT and at least you will not waste a year for preparation of CAT.