How do I add items to my C++ based set, from my HUD Widget?

I am trying to add items to my c++ based Set “PlayersKenoCard” from my HUD class; by using the OnClick event for each of the 80 buttons I have.

However, I cannot see the items of the Set, and it seems that it is not actually adding the items to the set.

How can I see if the items are being added; or add them to begin with?