If you installed it properly it should work, so I suspect something is not quite correct.
Have you tried using Terrasync ?
All you need to do is click on the box next to 'Download scenery on the fly' on the front page of the Mac OS X launcher. Then start a flight.
The first launch may give you the same picture (sitting on water with no scenery), but if you wait for a couple of minutes, then quit and relaunch FG, you should have the scenery downloaded into your Terrasync - Scenery folder. You may have to do this twice, but it usually works on the first effort.
Let us know how it goes.
Time flies like an arrow
Fruit flies like a banana