As a minor note, 20 deg. C (68 deg. F) is on the high side for a lager; that's more typical of ale fermenting temperatures. Lager yeasts generally do best around 13-16 deg. C (55-60 deg. F) for fermentation and around 5-7 deg. C (41-45 deg. F) for lagering. While the higher temperature probably isn't disastrous, finding some way to control the temperature better is something to consider for the future, especially with lagers. One of the reasons I generally brew only ales is because I don't have a way to keep a lager down at the appropriate temperatures (yet).