A temporary resolution

I guess that works...

If I ask the page to go fullscreen when the user clicks on the "run game" button, the arrow keys work great!  Not sure if this is a better solution to just redirecting the user to the actual Scratch page, just yet

There are also difficulties with getting out of fullscreen, I'm afraid.  When I click "escape" it escapes full screen in the actual embed instead of in itch.io.  

Nothing comes easy, does it?