A WidgetComponent Spawns a widget automaticly based on the class you give it or a direct Widget pointer. SetWidgetClass(TheClass), SetWidget(ThePointerOfExistingWidgetYouCreated).
I also noticed you dont have a WidgetComponent at all. You might want to create one in your Constructor and SetVisibility(false) aswell as SetWidgetClass(MyWidgetBlueprint) and in your BeginOverlap SetVisibility(true) / EndOverlap SetVisibility(false)