You have borrowed some books from your university library but you have not returned them yet Write a letter to the library officials and in your letter describe what happened express your sincere words of apology and offer what you can do to make it up

Dear sir/madam,
I am writing to apologise about keeping books that I borrowed from college library three days ago which is longer than acceptable.
I have found myself in this unwonted situation for a reason. my close relative was very sick and I had to go visit him at the hospital. I intended to return the books immediately after I get back to the college, but unfortunately I love the books on a train on my way to hospital to the library. it will take me about two days to get them back from "Lost and found" department.
I understand that other students may need those books and deeply apologise for the inconvenience. I will try to return the books as soon as possible. Please don't revoke my library privileges. I promise that it will never happen again.
Your Faithfully,
Nidhi Mehta.