Sorry to hear of this problem WildBill, it sounds all too familiar... My 2015 C5 cap had key issues too but eventually would open, then you had to fight to get key out. The other problem was severe leakage when I tipped the bike one day. Fuel just dumped down the side of the bike like there was no cap at all.
Soon as I got home I ordered the Hitchcocks non-locking screw on coversion kit, which I instantly fell in love with.
I have just been waiting to hear that this cool looking cap was also crap. If an alternate non-locking cap can be found I want it.