Difficulty with modify > contract on a saved selection
I selected part of a photo (a tree) then copied it to a new bank layer (Cmd+C then Cmd+J) and then saved it as a psb file. When I opened the file later I wanted to contract the tree by 10 pixels but can't find a way to do this and save the result. I select the tree then modify > contract and can see the marching ants have moved in as expected - but what command or sequence can I use to then save this contracted (smaller) image? Everything I've tried so far just reverts the image to the original. Thanks in advance and hope if there is an answer I understand it!
