Was this "zoom" constant or just when you clicked on a level in the level selection?
Added a few screenshots to help
What's your monitor's resolution?
Playing on my laptop 2880 x 1800
That's weird. I thought your problem might have originated from your monitor being to small in terms of resolution (I have 2560x1440) as I experienced the game in the browser a bit smaller due to it being 1080p.
Nevermind, hope it doesn't happen again.