it will be blended in you wont even notice it. No need for the whole rear quarter, far to big of a risk for a mismatch. any good body shop will do a good job and blow it in around the arch.
Oh and dont try ourself as youl need to sand it back to bare metal youl have to e-prime it, prime it, metallic basecoat which isint the easiest to spray to get the metallic to shine, and then clearcoat which isint easy to spary over metallic you dont just whip it on, you have to do light coats and build it up.