You have a good profile. Your high GMAT score will make up for your low B.Tech grades. As long as your story is consistent, and you have shown ability to do hard work in the past, a slight aberration in your grades won't affect your application much.
As far as extracurriculars are concerned, they show that you're outgoing and initiative taking person. But, you would have to highlight your achievements as compared to mere participation in events. If you are passionate about any cause (blood donation, women, education, etc), take up a leadership role, and lead from the front. It is easy to become a volunteer.
If you can translate all your achievements into good essays, I think you can easily get to the interview stage. If I were you, I would focus all my energies on the application essays. If I were you, I wouldn't take up GMAT again. Focus on essays.
Visit schools. Speak to current students and alumni of your target schools. Use LinkedIn if you cannot find contacts at those schools. Get your application reviewed, and re-reviewed by the alumni. It helps.