Select the layer again. Select All command.

interior illustration

Now choose the round marquee tool and holding the shift key select here.

It will leave only what you haven's selected.

interior illustration



interior illustration

A little transform and further this one too.

interior illustration



interior illustration

And use the
  
same white to transparency gradient.

Be patient! Any illustration is built form small pieces.

interior illustration

Now you remember that we had 2 copies of the layer. Forget it :)!

1 - Fill the Background with pure black.
2 - Turn one of the copies off visible.
3 - Erase the layer.

interior illustration



interior illustration



interior illustration



interior illustration