I recieved a key for a parcel locker and i noticed the lock was slightly turned clock wise and the key wouldnt go into the lock. Then I noticed the door could be opened without it. Being sunday now what do i do with the key?

Do i put it in my mailbox with a note or wait till monday and call the post office. Should i still leave a note in my mailbox for the mailman? I was expecting and tracking my package closely so i still got it thankfully. But dont want to have the key