If I told you to join the military and earn a Bronze Star would improve your chances to get into b-school, would you do it?
If I told you to become a nationally ranked athlete and compete for the Olympic trials, would you do it?
If I told you to start your own company, get it VC funded, get national media coverage for your brilliant idea, would you do it?
If I told you to quit your job, move to Tibet, risk your life by joining a clandestine Tibetan Independence organization, would you do it?
In other words, regardless of whether you are "good enough" to get into a certain b-school or not is not for you to judge.
What you should be doing is being the most accomplished person that you can be in the areas that you find most personally meaningful or fulfilling, and then letting the chips fall where they may. All of the "achievements" I've listed above are certainly exceptional, but NONE of these people did it with the idea of "bettering their chances to get into b-school." They did it for its own sake, and they are accomplished people because they are exceptionally gifted or talented at what they do (and as you know the delineation between hard work, talent and luck is hazy at best).
So the answer to your question is, to be as talented and accomplished as you can be -- and whether that is good enough to get into b-school isn't for you to judge (because it's not really in your control anyhow). If you feel you're doing all you can now, then continue doing that. If you feel you can do a lot more, then do more (and figure that out for yourself what "more" is for you).
As for your GPA, there's nothing you can do about it, and you've aced the GMAT. Don't worry about it.