Same, I stopped there due to that.
Also, it doesn't save?
Well, apparently you can just click any level at any time. Great! And now it's clear why level 4 only has 219/220 required diamonds. That's the end of the demo. There are no more levels.
There's no exit-level button (well, 'Restart' IS that), and if you try any levels past 4, you're stuck and have to refresh the page.
There doesn't seem to be much game here yet.