You said you were putting this in your portfolio. Does it not bother you at all that you will show this as a 'painting' you did and use this portfolio to get a job or into college (as i am assuming thats why you have a portfolio) yet it wont bet the painting you did, it will be an altered work. and its not even altered by your own brush, keeping it as a painting you did, its now been altered digitally. why didnt you just do the whole thing in photoshop if that was your original view? did you not have the technology to get the perspective correct when you painted it?
not trying to bash what your doing (or even say its wrong), and this isnt meant as a personal attack. Just trying to make a point that not only is what you did different from what lucas did to an extent. But also that the changes you made do have an effect on your work and perception others have of it/you
-Darth Simon