Thank you for bringing this to my attention.
Firstly - I've lowered the standard web resolution to 960x540, which should probably help, but if it doesn't - change the zoom level in your browser. It will force the game to readjust to the new window size on this page.
Secondly - the game is locked to a 16x9 ratio because I haven't bothered with UI scaling for now, which was an unfortunate mistake on my part. This may... potentially mess with some screen resolutions. It wasn't meant to be played on a phone too.