I got myself into a big mess...?

Go ahead and say what you need to say! You'll feel so much better and even though her parents treated you nicely that was them not her. You can still be respectful to he parents. Every parent knows that not everyone will like their child and usually parents notice what their children do. They will not hold it against you I mean yes if they won't have you over out of respect for the daughter but they are grown ups and they should understand.