Oh, I'm sorry if I have formulated myself poorly.
The trapes is on a layer on its own. Use the fuzzy select (Magic wand) tool to select the inside. Then go to a new layer. Your selction will be kept. Then feather the selection and follow the tutorial.
Make sure you are on the layer with the trapes whilst using fuzzy select. After that, get a new layer.
The deselection is weird. It shouldn't happen. You feather edges with selection>feathered edges or something like that. You'll see it when it shows up.