Ongoing struggle with GMAT

Hi,

I took the GMATs for the first time back in March; my score was low, and I was not in the right frame of mind when I took the test. A week prior, a relative passed away unexpectedly. I decided to study hard for the following months. I just took the GMATs for the second time last week end--scored 510. I was very surprised with this score. I took six mock exams, and scored between 570-690. So, I felt very confident that I would break 600. I scored much higher in the math section, and this surprised me because I am usually much stronger in verbal/language areas. On my first GMAT, both AWA's were 6.0.

Here is what I have done to prepare:
- Took a GMAT prep class
- Used the Official Guide (I've done about 700 of the problems)
- Used Princeton Review books
- Used Kaplan books
- Used Barrons books

I need to break a 600 in order to be accepted into the MBA program in which I am interested. I am retaking the test at the end of July so that Admissions can still process my application for consideration for the upcoming year.

I have been worried and stressed about how I should study for the test now; I feel like I just keep buying books. This site looks like it will be a fantastic resource. I would really appreciate some feedback and help in forming a more effective study strategy to help maximize my score.

Thanks.