There's two separate questions she asks at one point, to get her bad ending you need to give a specific answer to both of them, otherwise you get the good ending.
Aye, I think that's where I went wrong somehow. I did choose those specific answers, but still had the good ending for some reason. I figured that maybe it was because of me picking "bi" instead of "gay" all the way back at the theme park, but I've honestly no idea.
Thanks. I did manage to get to her bad ending somehow eventually, but to my knowledge I didn't do anything different from my other try before that, though I probably just did do it wrong.