So you relied on the OG review sections for math and verbal to study? If so, then I think that we have just identified one of the major reasons for your score. The OG is good practice material, but the short review sections are unreliable for delivering great results. You definitely need to rely on proper guidebooks. First, see here:
best-gmat-books-77703.htmlSince you seem to struggle more with verbal, look into the Powerscore CR Bible and the Manhattan SC guidebook.
The Manhattan math series seems to be the most popular source for the quant section, but they're expensive and might not be totally necessary for your circumstances; you already studied a good bit, so five math books might cause GMAT fatigue. So look into the Kaplan GMAT Math Workbook.
A GMAT course is an option if you need the discipline and structure that a class environment can offer. It's also something to consider if you strongly feel that you need additional, outside help.