In that case, unless there two different designs of shoe with the same diameter, and you have the wrong ones (unlikely!), there's something wrong with the way in which you're trying to fit them - which is holding them further apart than they should be.
BTW, *please* try to use the right terminology for the sake of other readers. As has already been pointed out by someone else, what you have are brake *shoes* - not pads, and they fit inside *drums* - not rotors.
[The rear brakes on your car are in fact *two* separate braking systems - disc brakes with hydraulically operated pads to stop you, and drum brakes with manually operated shoes (via the hand-brake lever) for parking. It's the drum (parking) brakes which are the subject of the discussion. OK, the disc (rotor) for the disc brakes happens to be made from the same bit of metal as the drum for the parking brakes - but that's beside the point!]