It is given in (Fatawa A’alamgiri, Vol 4, Pg No: 366)
Translation: A person borrows or hires a means of transport, boards it, then gets down in a lane and leaves it open (i.e. unguarded) and enters the Masjid for offering Salaat. During this time, the means of transport is stolen then this person (the borrower) is responsible for it i.e. it is compulsory that he pay back the full amount to the owner.
If the borrower hands over it to somebody for safekeeping and the means of transport is then stolen then he is nor responsible.
In light of this, if you had kept the scooter in a safe place and had properly locked it, then you don’t have to pay any fine, but if otherwise, it is compulsory for you to pay back the full amount of the scooter to the owner.