800 grit or better is 600. Just don't use the 600 P sandpaper. Really hard to tell what you have there and if you're blending the paint on the 1/4 panel just sand the door and blend the pant into the door and clear the whole door. and 1/4 would be best.
Also I have no idea what you did to blend the paint into the 1/4 panels but if you just used single stage and blended that into the 1/4s it will after time fade really fast. need to clearcoat the whole panel that you painted.
Just my thoughts.