New user - layers question

[Allen]

I actually want to add a border to the image itself and I just noticed the the border adds itself as another layer at the size of the background image. How can I add a white border to a small layered image. If I have the layer selected (yellow dotted line) and I do Filters->Decor->Add border it adds this new layer; maybe I am trying to add a border to my small image incorrectly?
(also can I attach images to these chats, might be easier to show you the snip image)