Yup, I've tried that, actually the first thing I did... But to no avail... Here's a video of it to see if maybe you can infer anything?
I see! Maybe try zooming out in the browser before or after FULLSCREEN? Usually, you use CTRL and minus (-) sign on the keyboard to zoom out.
Yeah I've tried zooming in and out and that didn't work... Luckily I was able to land my hands on a desktop and got to play your game... Great work!
So sorry for the inconvenience you had to go through! But I am glad you liked it in the end :)