Hi Emilio95,
Test Day is a rather specific 'event' - the details are specific and they matter, so you have to train as best as you can for all of them. The more realistic you can make your CATs, the more likely the score results are to be accurate. The more you deviate, the more "inflated" your practice scores can become - and that's what happened here. By skipping sections, taking the CATs at home, etc., you weren't properly training for the FULL GMAT 'experience.'
Test Day involves a variety of really specific steps and parameters (including steps before the Test even begins - such as leaving your home, traveling, etc.). Every factor matters, including the psychological ones. When you sit down on Test Day, you KNOW that you're going to be in the Computer Lab for about 4 hours - but if you're just taking individual sections (or taking a CAT without the Essay and IR sections), then you KNOW that you'll be done in 1-2 hours. The attitude and energy that you use during practice will NOT be a match for what you'll need on Test Day, so it's not a proper way to practice. All of the 'differences' involved in how you took your CATs could explain why your Verbal Scaled Score dropped on Test Day. You weren't properly prepared for THAT full day, so your score fluctuated.
Thankfully, those are relatively easy issues to fix - now that you've taken the Official GMAT, you know the EXACT details of what happens on Test Day, so you can better train to mimic those details during your CATs. With a 590, you're closer to a 640+ than you probably realize, so the question right now is how 'efficient' you want to be with your studies over the course of the next month. You could potentially hit your score goal simply by studying in the same ways that you have been studying. However, the inconsistencies in your scores imply that you would likely benefit a great deal from a more consistent, guided study routine.
1) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich