As stated on the game's page, it is designed for a 1080p screen minimum, and it is not designed with Android or other mobile devices in mind unless they have the resolution required to play the game in landscape (ie, a tablet). If you are on a 1080p screen, you may need to check if your system's display setting are defaulting to a zoom-in (some laptops do this, defaulting to 125%). You can also manually adjust the game's zoom by whatever method your browser supports; usually ctrl+scroll.
If, however, you are on an Android device, then the page will have warned in advance that it is unlikely to work.