HELP THINK PARENTS KNOW

We are only 16 btw, So I was at my boyfriends house and we were having sex and we think his dad heard because we only could hear him coming when he was like 5 seconds away from the bedroom door so we quickly stopped and he came and said night... we are worried he is gonna ask us what we were doing and we don't know what to say... cause we think it looked heaps obvious what we were doing ! what can we say if he asks??? šŸ˜«šŸ˜« sooo embarrassing and awkward šŸ˜•