Hi assaffff,
A 600 is a strong 'baseline score' (the average score on the Official GMAT hovers around 540-550 most years). When you took this CAT, did you take the ENTIRE CAT (including the Essay and IR sections)?
With the timeline you've described, you've given yourself 2 months of full-time study, plus whatever additional studying you do until mid-August. That could very well be enough time for you to hit your score goals, but we'll know more as you continue to study.
When it comes to GMAT resources, most GMAT Companies offer some type of free materials (practice problems, Trial Accounts, videos, etc.) that you can use to 'test out' a product before you buy it. We have a variety of those resources at out site (
www.empowergmat.com). I suggest that you take advantage of all of them then choose the one that best matches your personality, timeline and budget.
If you have any additional question, then just let me know.
GMAT assassins aren't born, they're made,
Rich