And the re-homing of Christmas puppies begins....As Angelbaby suggested, I would contact the breeder. A responsible breeder would want that puppy back (then again, a responsible breeder would have checked to make sure you had Landlord permission before placing the pup with you, since that is such a HUGE problem with this breed)
Have you thought about trying to KEEP the pup? If you speak to your Landlord and find out what his issues with the breed are, perhaps they can be over-come. If it's an insurance issue, you can offer to get a Renters policy which covers the dog. State Farm and Farmers are two companies that offer those in my area. I can give you the name of my insurance agent, Eric Einhorn, of Einhorn Insurance, he can get you coverage.
Or you could move. If you can not return the pup to the breeder (say you got the pup from some BYB or off Craigs list) and can't swing the Landlord conversion and end up re-homing her, please, please, please make sure her new owners have permission for a Pit Bull type dog or own their own home. It's very hard on a young dog to get bounced around to multiple homes.