Hi hugdor,
Since your current Test Date is in just over 3 weeks, that amount of time will probably not be enough for you to make the necessary improvements and score in the 600s. As such, you should really think about rescheduling your GMAT. As it stands, you could take the GMAT as scheduled and then take it again later - it will just cost you another $250.
From what you've described, you've been studying inconsistently for about 2 months. That type of effort probably won't be enough to get you into the 600s, but the GMAT is a predictable Test, so if you can make the necessary adjustments to your schedule (and study in a bit more of a consistent and rigorous fashion), then you CAN train to score at a higher level.
1) Do you have a specific score goal?
2) When are you planning to apply to Business School?
3) Do you know which Schools you plan to apply to?
GMAT assassins aren't born, they're made,
Rich