[HayZee518]

try a 320 grit open coat aluminum oxide sandpaper with a palm sander. use a snap line and apply a blue masking tape along that line then paint. remove the tape before the paint is dry. when that coat is thoroughly dry use some more blue masking tape along the line and paint the other color. the thicknesses should be about the same so it won't show the lap line, it should butt up against the first paint coat.