hi gparmar16, there's a thread in the GMAT Section that explains whether one should do or retake or not. Seeing how confident you're describing your GMAT experience, it does seem like that you could have probably done better. However, I really don't think that a 720 or a 750 is any different in the adcom's eyes when you're applying to the top schools in the nation. The GMAT, in my opinion, is used as a benchmark, that as long as you have the score schools are looking for, whether you achieve 800 is not in the question anymore (i.e. Stanford rejected 800s last year). I believe a 720 is already competitive for all the schools in the world, since even H/S/W has an average of around 718. I would focus more on the application at this point, rather than trying to boost your score another 30 points (let alone the danger of having it go down...)
If you're gun-ho about re-taking it, Knewton offers its course for free if you don't improve your score by 50 points. Seems to me a win-win situation for me. If you're going this route, make sure you read the terms and conditions as I don't know anything about Knewton directly.
last but not least, a Q49 is only a 83 percentile?!?! That's a bit too low for a Q49, imho...