with very fine wet and dry(1200+), used wet wait about a week then gently rub off the new paint, being carefull to only just remove it and not go throught the laqour if its metalic or paint if it aint. go to vauxhall and get the proper colour touch up pens, put masking tape about 1/2 mm each side of the scratch and touch it up along the length if your car is a straight colour do a few coats till its ever so slight above level, wait a week, but you can take the tape off. then with fine wet and dry, used wet, gently rub back the raised line till level and teecut and wax back till nice. it may not be perfect but can be almost un-noticable if done carefully. and lesson learned dont buy paint from said shop, im sure its mixed after a morning on the thinners. metallic is a bit more difficult but same sort of idea but cover with colour till just below level and use laqour to get just above level. the closer you can get the tape to the scratch i.e the thinner the bit you paint the less noticable it will be. wait a bit other people may have better ideas but ive done it like this in the past and after a while and a few cuts and polishes forgot where it was!