Help, it has to do with my school library book?

Okay, I have a book report due tomorrow, and I lost the dang school library book for it. So, I lost the book, and can't do the book report. The report is for the librarian. Would it be right to go up to her tomorrow and tell her "I'm sorry, but I lost the library book for the book report you igned"? "Can I pay you back?" I am also going to ask if I can get another book and turn it in on Monday. I never lose anything. I think someone took it, because I was in Study Hall, and whenever I turn around, something is missing. Would she let me extend the report?