I had the exact same problem as you. The screen was cut off from me as well. I have had this problem with multiple Unity games I tested in other game jams, and it kinda sucks... But I was actually able to complete levels 1 and 2 still! :)
So yeah, Some Unity games played on the browser just get cut off. There are ways to fix this, but I find a lot of people unfortunately forget to do this and it kind of ruins the game.... Hope this helps.