A friend has touch up her black Corsa with a touch up pen after a getting a parking scratch on her bumper. Its plastic and the scrape took about a 2 inch scrape of the paint showing the white plastic. She has touched it up with a pen but the finish if dull and slightly raised. It looks like somebody has rubbed lumpy shoe polish on it and its dried with out being buffed up. I need a quick fix before her Dad sees it. Needs to be easily available from Halford, Motorworld etc. Any ideas cleaning guru's? Thanks in advance from Sarah (my friend).