It's designed to be the right size for 1920x1080 screens, but if you have a lower resolution screen, hit the fullscreen button in the bottom right and it should resize to your device.
remember that we're also playing this in a browser.
I guess I'm just used to the games not taking up the whole screen. just remember that if you're having trouble scrolling down to the full-screen button, the menus in the top-left won't nullify your scrolling.
