there's no such thing as a aftermarket oem bumper cover it ether aftermarket replacement bumper or OEM (original equipment manufacturer) and most of the time they do not fit properly as redturboeclipse said you should have fitted it first and then painted it.
the vinyl cutter is also called a plotter, and after you cut and weed out your decal you can buy a two part epoxy called diamond coat that will create that dome effect.