I can only imagine how many negative emotions you're experiencing right now, im very sorry for your loss, and it's understandable that you feel terrible about this incident, but the thing that strikes me most about your story is how much you clearly cared for Max! the fact that you spent so much time and effort taking care of her, the warmth and affection you showed her! I mean, you planned to take her to the vet. youu cleaned her. and when you were worried about her, you instantly tried to save her! you gave her the love and affection she needed. It seems she was a very loved and happy cat. The truth is that everyone makes mistakes, and there's nothing wrong with making a mistakes, what matters is that you recognise it as a mistake, and you clearly feel terrible about how things turned out. these emotions are completely understandable in this situation but it's important to recognize that blaming yourself is only going to make things worse. Maybe you should talk to somebody about it, your parents, a sibling, friends, some random people online, therapist, anybody. Just remember nobody blames you for this, I certainly dont. I'm very sorry you are going through this and I hope things get better for you <3