Yes, timing can KILL your score - you can learn a ton of stuff and still have your score go nowhere. :(
Before I get into advice, it sounds like you have a fairly significant timing problem and I have to tell you that it usually takes people a good 4 to 6 weeks to fix major timing problems. Often, people will go too far in the opposite direction at first (too fast), and then have to learn how to get back "to the middle." You say your test is in 3 weeks. If you have the flexibility to take a little more time, do so. If not, you'll just have to do what you can in 3 weeks!
First, let's address mindset. Think of this as a tennis match, not a test. You're going to win some points and the other guy is going to win some points; you're not going to win them all, right? Your goal is to put yourself into position to win the LAST point. Translated, that means you have to put yourself in position to answer the last question - you have to have time to address it (though you don't literally have to get it right). Otherwise, you've lost the last point, and by extension the match. When the other guy hits a winner, don't go running after it so fast that you hit the fence and injure yourself, thereby hurting your chances on the later points. (Translation: don't go way over when the problem is too hard.)
Instead, say "Nice shot!" (and mean it!) and move on to the next point. If you do not change your mindset on this, you are not going to get the best score you could get on this test.
Next, use this article to analyze your most recent practice tests and really figure out where you're losing all that time right now - your first step is to KNOW, pretty quickly after a new question pops up, that this is one of those ones where you're in danger of spending too much time, so that you can be extra-alert.
http://www.beatthegmat.com/mba/2011/02/ ... sts-part-1I think you would also benefit from a timing exercise: learning about how long one minute is without looking at a watch or stopwatch. Note that the below detail specifically applies to quant and quant timing.
If you don't have one already, buy yourself a stopwatch with lap timing capability (or use your smartphone or an online program that gives the same capability). When you go to do a set of problems, start the stopwatch but turn it over so you can't see the time. Every time you think you're one minute into a new problem, push the lap button. When you're done with that problem, push the lap button again, then repeat the process for the next problem. When you're done with the set, see how good you were - and whether you tend to over or underestimate. Get yourself to the point where you're within 15 seconds either way on a regular basis (that is, you can generally predict between 45 sec and 1min 15 sec). Also check your timing for the entire question, of course.
Now, how do you use that when doing problems? If you're not on track by one minute, make an educated guess** and move on. (The general idea is that if you're not on track by the halfway mark, you're unlikely to figure out what's holding you back AND have time to do the whole problem in the 1 min you have left.)
** This also requires you to know HOW to make an educated guess depending upon the type of problem and the content being tested. So that's something else to add to your study: how to make educated guesses on different kinds of problems. And here are two articles to help (one for quant, one for verbal):
http://www.beatthegmat.com/mba/2010/07/ ... s-on-quanthttp://www.manhattangmat.com/articles/e ... verbal.cfmAnd here's another article on time management:
http://www.manhattangmat.com/articles/keeping-pace.cfmSo, lots of stuff to work with there. Try it out and come back here with questions.