Hey emk,
Big week! Hopefully you're enjoying the adrenaline that comes with an impending challenge...
I don't know that I can give you great advice on how to increase your speed over a few days (at least not in a paragraph or two email), but I think you can definitely boost that score by paying attention to the errors that you've made while rushing. Since it's likely that you'll be under time pressure on test day, I'd advise making a quick checklist of your common errors so that you can do a quick scan for those before you submit your answers. Mine, when I took the test, was very Data-Sufficiency-heavy:
Positive (don't assume that a variable is positive...consider the possibility of a negative)
Integer (don't assume that a variable is an integer...consider fractions/nonintegers)
0 (make sure to consider the possibility of 0)
Sufficient (your job is to determine whether the information is SUFFICIENT, not whether the answer is "YES" - if you get a firm "NO", that's sufficient)
? (make sure to answer the right question on PS questions - if you solve for x, make sure that they're not actually asking for y)
That 5-point quant checklist helped me catch a few potential mistakes early, and from then on I was pretty in tune with doublechecking errors without the list. Those are pretty common mistakes, and you can probably find a few others that you've frequently made in practice tests so that you can be aware of them. Usually these kinds of mistakes come when you're rushed for time, so building in a 2-3 second double-check can help you to avoid those traps...
Good luck this week!