Can't you activate fullscreen? Itch should provide a button on lower right corner and your engine is unity, is it not?
You can also place an element (picture) above your game to keep distance, the user tools should scroll away by that. Do not ask me how, I only saw that on some browser games. Also, if you zoom the browser, the css of itch makes the user tools a top row element. But your game placeholder zooms with it, probably the actual game too.
But seriously, the layout of the pages should be a tiny bit different. The user tools annoy on lots of game pages. (that is the name of the element #user_tools)