Sorry to say it this way, but I would reconsider passing the GMAT next week. Could u still postpone it?
Your low 40s in Q could be due to several reasons, hardly fixed in 1 week:
> lack of basic : it means 1 month minimum to learn and apply all new things learnt
> time management problem : it needs a lot of practices in real time condition
> careless mistakes : it does imply to examine what in u, background included, make u create these mistakes... false assumption on variables percieved to be integers when they are real numbers...
> technics to finish a question: practice, practice and practice
In addition, the last week should be used to build up your confidence not to burn out by learning fastly and hardly a maximum of things on the Q section....
All in all, I'm perhaps wrong.... It's only u who has the keys of this !
Good Luck !