Don't know if you can manipulate the css file, but if you could add this rule, your problem might be fixed.
#canvas {
width: auto !important;
height: auto !important;
}
Apologies for how long it took to get around to this. The game should now resize if it opens in a window, the visuals don't look great when played at large sizes though haha.
Much better, thanks for the improvement.
