I think this choice is completely up to you and how you feel about the animals well being. It takes a big person to see that fact that they can't properly provide for an animal so I give you major props for realizing that and admitting it not only to yourself but to everyone else. Honestly if I myself were in your position where the breeder (N.E.R.D.) is willing to take the animal back that's probably the route I would go. And since they're giving you store credit they have a ton of other animals that are way easier to care and provide for. You've already taken the first step in realizing there's an issue. And that's a big step. Whatever you chose to do I'm sure it will be the right choice and it has to be your choice not ours.