Electrical double layer
The phrase "retain those 2 electrons" is wrong.
Metal surface has positive potential in solution, 
but this doesn't mean that lost electrons are concentrated somewhere.
Electrons don't form layers. You can think of electrons as much more "volatile" things than ions, they may discharge everywhere depending on potential, for example, to reduce Zn ions in solution.
So, surface is charged positively and hence first ionic layer is negative.