I have also never used Open Library. The two Overdrive driven ebook libraries that I do use each have a "My Bookshelf" link once I log in to my account. Clicking on that link will produces a page of all the books that I currently have checked out. Each has a download button that can be used to again download any book that has not expired. As others have said if you don't want the book and just want it to be removed from your books checked out list that will happen automatically on the expiration date.