You've got to develop an internal sense of time. The good thing is that you've got time to do that before the test.
Start doing practice problems with a stopwatch next to you, and record the time it takes you to work through a problem so you can visualize how long it actually is.
Then, as you study and become more adept at manipulating problems and learning more material, start pushing yourself to find the solution by 2 minutes, or 3 at the maximum. Stick to this strategy and guess if you find yourself going over 3 minutes - I struggled with this quite often - I would spend 7 minutes on a problem I would eventually get wrong, leaving me no time for problems that I could get right.
You've just got to learn to sacrafice a few problems in order to put yourself in a better position for the test overall. Time monitoring must be ingrained in your head by test day.