I have been having the same problem on Mac OS X 10.8.5. I've tried defining different paper and margin sizes, but did not find a difference. The right hand column (formula/entry option) seems to stay at the same width regardless. If you print in portrait mode, approximately 1/3 of the available page width is not used for the formula column. This becomes even more pronounced if you print in landscape mode. In that case about 1/2 of the available page width is not used.
If anyone has a solution to this, I would love to hear it.