I think you are still selecting the entire board cut out shape.
Note the dialog you get - it is called "Drafting Properties". In my example it is called "Drafting Edge Properties"
You need to enable "Edges" in the selection filter. A quick way is to Right Mouse Button click and select "Select Board Outline".
Also - you cannot modify board outline if your design rules is on.
I guess it is not possible to attach a file?