Am I an actual doormat? ?

I have recently allowed some of my friends to use my public library card as they don't have one themselves. I have renewed said books online about 4 times which is the max limit. I told my friends the due date a week before the actual date. A friend (friend B) wasn't able to and decided to ask me the day before the due date if I could return her books for her, which I said was ok, she had also asked me to return a book for her and then take out again, which I did. I then gave her the book back. I then checked my library account online several days later and it seemed a book hadn't been returned and i was being fined as, I had told my friends to look for the book and friend B told me it was her book and told me that she had returned it herself and I told her i would email in to check if it had been returned and It hadn't been, so I texted her later on and asked her when she had returned it and she had told me, 'I had given it you?! when did you return it'? which confused me so I asked her to look for it, and she didn't get back to me so I texted her the next day asking if she found it adn she said 'let me check now' and I asked a few hours later, 'how about now?' and she said 'found it! my dad must have moved it when cleaning!' and at this point I had accumulated a small amount in fines and I told her to return it ASAP as I didnt want to risk having my account blocked. 4 days go by and I ask if had returned it and she told me she was planning on returning it the next day.