Hiya,Dont use a touch up, it comes in two parts including the lacquer and results are awful. Better to match your colour at a paint makers or bodyshop and have them mix it for you. They can also match the code, which is usually on a silver sticker inside the rear hatch. If not there, try all the other shut areas, doors, bonnet etc. Make sure they make it a two pac mix, this way the gloss is already in the paint and you only have to apply it once. It normally costs a £5 or so for a small plastic pot which will last years as long as you seal it well.
MOST IMPORTANTLY, apply the paint with a pin or cocktail stick and 'fill' the hole by dropping the paint into it and moving it with the point, to fit the shape of the chipped area. You just have to get a small bubble of paint on the end of the pin.
DO NOT PAINT THE CHIP!!!!!