GMAT Strategy

I'll start by giving a little bit of a background on myself. I've worked at a big four accounting firm for the past 2 years and would like to go back to grad school to change careers. I started studying for the GMAT in January while trying to balance work(50+ hour work weeks +travel). I was aiming to take the test in July.

I've purchased all of the Manhattan and Kaplan materials and have been studying on and off since then(1 hour per week night,4-6 hours on the weekend). I didn't want to take the diagnostic test right away because I had to brush up on the material. My first plan was to go through all of the manhattan and kaplan books to review the material. I dedicated 1-3 weeks for each Manhattan book while reviewing a couple of the kaplan books on the same material.

I started in the 2nd week of May to go through the Manhattan Verbal and Math review books and have been keeping an error log of the type of problems I am missing. I have not completed all of the books but I have about 30+ problems completed for each type of question and have scored about a 75% of DS, 90% of PS, 93% SC, 78% of CR correct,and 80% on RC.

I started to take actual practice exams on 6/1. I scored a 410 on my first practice exam(GMATPrep Exam 1). I ran out of time with about 10 problems left on the Quant section. The verbal section I barely finished on time. I got a total of 15/37 correct on Quant and 26/41 correct on the verbal section. Needless to say, I am completely crushed by this first practice exam score since most people score considerably higher than this without any preparation. Does anyone have any suggestions or strategies they recommend me taking? I almost feel like giving up.