To be fair, Craig, the lager style is not known for this quality and this is for a good reason. There is not really sufficient residual malt in the brew to support good head retention.
The kit you have made makes a good version of the lager style, but if you want a "head" on your beer, you are better advised getting a 2 can Ale style kit, brewing to 20L and making absolutely sure that there are no detergents left on the surface of your glass.
Good luck with your brew, it will improve in all respects over time, even with head retention.