I had the same problem, you have to resize your browser window so that the scroll bar disappears, then you can use the + and - key ingame to scale to your liking, it works very well.
The game is really interesting and a real challenge! It would be cool if you could turn the blocks in the third axis: right now, you can only break layer by layer, if you could fit the i-block vertically to solve 4 layers. (then again, this might be too complicated....
In any case, great game!