Hi galby,
To start, a 680 is an outstanding initial CAT score (the Average Score on the Official GMAT hovers around 550 most years) - so assuming that you took this CAT in a realistic fashion that matches-up with how you will take the Official GMAT, then you are likely already a really strong critical-thinker (which is great!). That having been said, many GMATers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so if you are going to limit your studies to just 6 weeks, then there might be a limit to how much you can improve in that time.
Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on your timeline and your goals:
1) What study materials do you currently have access to?
2) Are you planning to take the At-home GMAT or are you planning to take your GMAT at a Test Facility?
3) When are you planning to apply to Business School and what Schools are you planning to apply to? If it's sometime soon, then what specific application deadlines are you facing?
GMAT assassins aren't born, they're made,
Rich
Contact Rich at: [email protected]