Why not bring it in and ask how much you owe them? Librarians are used to stuff getting damaged. It happens. I've done it. I left a book on the floor underneath an air conditioner that was leaking water.

Also, I check out 20 books at a time, too. I go in for one and then find three others while I am looking. I also return them late sometimes and keep renewing them so I can avoid bringing them back.