This game is just buggy as hell. In my second playthrough I manage to gather all the essential abilities (max Lust level, all abilities except hypnosis equipped) in day 19 before impregnating her. The first time I used the final option in page 4 I failed because the next few days her status was still "fertilized", and after I reloaded my save before the impregnating option and tried again, I managed finally to get the conception status in day 21, but then boom! The day after her status returned to "fertilized"! I seriously think that those like me who fail to reach the true ending must encounter the same issue like me.