First off, don't panic too much. You can always reschedule or exam, or better yet, take it again!
Timing is definitely difficult and it's something one should definitely work on. There are definitely strategies here. For quant, if you know what is required to produce the solution, and know it may take awhile and you may not even get it right anyway... just guess! Don't spend too much time on any given problem unless you're sure you can derive the solution. Also, be aware that the
MGMAT quant is significantly harder than the real GMAT. I ran out of time myself on
MGMAT, but was able to spare 10-20 minutes on the real GMAT quant. Nevertheless, I feel like taking practice CATs like the
MGMAT timed is very important in coming up with strategies regarding timing.
Same goes for verbal. Popular questions to guess on are sentence corrections where the entire sentence is underlined. Make sure your mind doesn't wander off during boring reading comprehensions and truck through it feigning interest in the subject. As you take practice exams you'll get better at determining both your pace and what type of questions are worth skipping (depending on how long it took you!).
In your boat, for the last week, I'd stop with practice questions and take full length exams, focusing on timing. I wouldn't just randomly guess on every 7th question, but look for strategic questions to guess on - ones that take long or ones you wouldn't correctly answer anyway. Also,
this thread has some interesting results - I won't say how you should interpret them, but it may be worth taking a closer look at the first few questions on each section. Also, very important that you don't run out of time (leave questions blank) but instead guess on the last remaining questions.
Best of luck!