I'll just quote my posts from few pages back.
I am not completely sure how I did it as I got that one started after I went past her pain threshold. I do know a few things that happened after that and will try to list them.
1. You need to get the quest from your aunt.
2. When you talk to Chloe, there may be an option where you state something about her enjoying it too much etc
3. Don't tell her about homework if this comes up, go back and talk to aunt and tell her that you don't think she is being punished hard enough.
4. At some point in here you need to find the homework.
5. At 15:00 Aunts mood needs to be neutral or in the red and you need to watch the spanking all the way through, then if conditions are right there will be additional scenes.
If at any time during this, you can't find the homework at 13:00 at interior location, talk to Chloe and if you have the option to pass the message on, do so then try to get quest from your Aunt again the next day.