Hello James,
Thanks for your lengthy and detailed letter.

Work-wise you seem to be in quite good shape, and for extracurriculars, although you say there isn't much, there does seem to be enough to certainly make a story or two out of them. At this point, if you are applying this year, what you really need to do is land that GMAT score you are aiming for. I don't how how many opportunities you will have to improve your profile in a fundamental way, but if you can either: get promoted, get a promise for a job post-MBA, or gain a leadership position/responsibility, these things can help greatly.