Strength, agility, and endurance greater than 5 open adult scenes after training. If you don't have them, make sure you have passed Miss Hatch's Level 1 event and that the conditions with stats are met.
Her Level 0 event is triggered when you walk into the locker room on Wednesday at noon. That's where you find out about her debt. And level 1 is when you go to the gym on Wednesday morning. There, the main character offers help and trains all the stats at once. If you have completed this and there are still no scenes, then send your save to me in Discord and I'll try to figure it out.