Yes! There are big penalties for not answering all the questions - just like on the real test.
There isn't one flat amount that's deducted - it depends upon your scoring level and how many questions were left blank. But you are definitely losing lots of points in this way.
At the very least, never leave anything blank - put in a random answer. If you put in random answers for the last few, even if you get them all wrong, the penalty is still not as great as leaving them blank!
Ideally, though, you don't want to be in that position either. So, you've got to fix the timing problems! Read these two articles and start doing what they say:
http://www.manhattangmat.com/blog/index ... to-win-it/http://www.manhattangmat.com/blog/index ... nt-part-1/