A simple undo function is currently in testing, and will be added to Pixelscape: Oceans later today. Your configuration settings will be reset when the update goes live, so if you've changed anything (sound, video, controls) you'll need to make those changes again.
It is a "simple" undo function because right now you can only go back 5 steps, and it can only undo objects you have placed, not objects you have deleted. The default key is "Z" (not ctrl+z).
If all goes well, this functionality could be expanded on later, but I wanted to get something in now to make creating easier for you all.