Parents know we are screwing

umm what should I do? how do I even start to talk to my girlfriend's parents now that they have found out that we have been fuckin..im not to worried bout her dad b/c he warned us bout her mom knowing and he didnt sound to mad...but what do I say and how would I approach the topic.

The parents are not going to walk around and pretend somethings not going on, and with that said the only way to handle it is as an adult and if they bring the topic up address and say your as responsible as possible