SPOILER ALERT! SPOILER ALERT! SPOILER ALERT!
You will have to replay this part of the game. Most likely CG you've missed is related to the moment where you're playing a video game against Asami.
If you win, you ask one of the 3 questions (and so on several times)
Play around with those questions to open several CGs.
One of the questions will unlock an anal option during the sex scene, which also will unlock another CG.