Motivation Needed

Hi All,
Long time listener, first time poster here. i'm trying to get a handle on where I am with regards to studying for the GMAT. Quant is my big weak area ( In that I didn't even have a lot of the concepts before beginning). I started studying in Jan 2011 and plan to sit the test 25 May 2011.

I've been working my way through the Kaplan Math Workbook and am gaining confidence in the concepts. However, I'm scoring about 50% on average (17/37), is that normal or am I right in assuming it's a poor score?. I am taking note of my weak areas: Ratios, Multiple Figures and Ratio/Percent Word Problems, am planning on ramping up my study from 8 to 15 hours a week through to May and work through every question and I get wrong (and at times those I get right too) .

I've recently purchased the complete Manhatten Review guides which I plan to start next week. Any advice on motivation/experience reports at this stageor study?

When I read reports of people achieveing a 640 score+ on their diagnostics test, I'm thinking I'm behind the trend.