As others have said, its still only very young and you will get set backs. Keep the retrieve training going with easy to retrieve items, the teddy, and then slowly move the dog onto other objects, fluffy toys are fun for the dog to retreive, i got my old dogs to retrieve shotgun cartridges, sets of keys, hammers, dog bowls, anythingg weird, ungainly, heavy etc BUT i only introduced unusual and difficult objects when the dogs were older. Also NEVER do retrieve training with a young pup in the presence of another dog. Keep it fun, light hearted and all sessions short.............