The first thing to remember is not to panic. Stay cool! Carnet's are no big deal, except for the deposit. If your bike is stolen, immediately have the police file an official report. With this you can approach your guarantor, who will impose a waiting period (perhaps one year), after which time you should get your money back. But the main thing is not to get the damned thing stolen. Take the bike to bed with you, if need be. You might get to like its body odour, and the bike likewise.
Enjoy your travels. No need and no fun to be paranoid.