Okay, so important question is if you're in a romantic route that isn't Asriel or in the friendship route, because some of my steps are from my experience while I was playing in Asriel's route. I'm unsure how you can trigger Rose Bastard but I think it's because for my character, I had it put that her favorite rose was yellow rose and she painted a picture of her yellow roses, and if somewhere in Chapter 4 (I think) you receive a bouquet of yellow roses with a cheesy poem, that means you're gunning for Rose Bastard's bad ending and that you must have missed either a clue or a romantic trigger with your chosen love interest (again, I'm unsure regarding the friendship route, maybe it's all about clues instead?) I hope this has helped in triggering your deductive senses, just save liberally and have some patience (that or you can rage quit without hurting yourself to relieve the stress)!