you can bring you library card to any public library and tell the staff. then she/he will use reader to read the barcode on your library card and record down the info of the book you have lost. sometimes they may ask you why when and where you lose the book (just because they are curious).
it will take them some working days (usually less than 3 days) to phone you back and confirm the price of the book. then you need to give the correct sum of money to the library. that's te punishment.
the library will not 減少your借出資料上限.
your圖書證will not留"案底".