Don't be so hard on yourself about the GMAT. Many people take the test two or even three times before achieving their target score. Hopefully your 2nd time around will be better
It strikes me that you are quite a young candidate. Sound like you will have 3 years work experience by the time of matriculation (on the lower end of experience). That does not mean you cannot get into top programs, but it does mean you'll have a tougher time demonstrating leadership capacity to the same extent as your peers who have 5-6 years of work experience going into the application process.
You should also be aware that you fall into the 'Indian male IT engineer' demographic, and that this means the competition is a lot fiercer for you. You'll need to find a way to differentiate yourself from your peers within this demographic. It's great that you have competitive chess experience - this will show your strong strategy/analytic skill set, but it will not really help you in demonstrating leadership and/or teamwork capacity as chess is a pretty individual game. Your volunteer experience is good, but not great -- volunteering each weekend for an NGO/charity does show commitment to your community, but does not necessarily demonstrate leadership capacity.
All in all, I think your biggest challenge is going to be to demonstrate your leadership potential - both inside and outside of work. So, even if you score above a 700 on the GMAT, I would recommend targeting programs such as HEC, Oxford, Cambridge, Rotterdam, NUS. Alternatively, I would recommend that you spend another year or two building up your leadership profile and then applying to more competitive schools if that is your goal.
Hope this helps. Good luck with the GMAT!
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