I am struggling to find a way to delete a game I have published (privately) as I only uploaded it to prove the process...
You'll need to send a note to the site administrator or wait for them to notice this message. I found out the hard way that publishing a game copies it over to a different part of the site, from where only the mods can delete it.
You could make it private by using ‘view/edit game listing ‘ and click on ‘only people I give a link to.’
That takes it out of public view.
Create a new game in Quest. Don't waste time adding any code to it.
Edit your listing, uploading the newly created game in place of the game you wish to remove. (That would at least get your current game offline.)