What do I do?! Need super help! please?

Ok so i went on a field trip and I brought a book with me thinking if I got bored I could read. I ended up NOT READING THE BOOK ALL DAY. I had it with me in the morning but I get up the next day and go to look for it and it's gone. I can't find it. It's a LIBRARY BOOK. It's also due this friday. My first plan was to renew it and continue looking for it, which I will do anyway, but after that I don't know. What if someone stole it or it fell out of my backpack? Also I have confrontation issues so how in the world can I tell the librarian I lost a book? I never ever ever mistreat books so I really screwed up this time. What if they don't let me borrow books anymore? Should I just buy them another book and keep the other one if I find it one day moving out of my house and going to college? Should I ask my teacher if anyone found a book on the bus or something? WHAT DO I DO I'M SO SCARED!!!!! please please help me.