The remaining Matt CGs are unlocked via another character's route at a different location. Instead of going to Matt's place in the evening, go to the club, and then spend the rest of the night with the bartender Griffin.
Didi is right that there will be more stuff to unlock with Matt in the morning, which is the update I'm working on now. I'm adding a new way to stay the night so you don't have to get drunk or hook up with Leo, you can just focus entirely on Matt. There are 8 new CGs for his "morning after" sequence, and most of them unlock if you start to nudge things in a romance/hookup direction. Your relationship with Matt can get a tad more physical depending on your choices...