Are you guys playing on HTML? If so there should be a fullscreen button in the bottom right hand corner. Let me know if this helps!
I was playing the windows version. I did manage to get the next best thing by hiding the taskbar and making the window bigger.
Luckily it was good enough that before long, I didn't even notice the top of the window showing. I really enjoyed it and think it was perfect for me since it was just frightening as many other horror games I've played (if not more) but short enough that I got through it before I could no longer resist the temptation to flee.
Thanks for making this game!