The shape of the head and eyes don't look really Maltese, either.
If you wanted a Maltese, please consider that although your pup is very cute, it may not have the lovable Maltese temperament, either. Chihuahuas are a very different breed, and might not like anyone other than their immediate human "parents." I have a cute 9 pound Chihuahua type who was rescued from a shelter as an adult, and I thought I was just going to foster him, but the start-up rescuer ghosted me. Charlie was a shelter favorite, but they probably never tried to do anything with him. After 12 years in my "custody," I have to say he is really so cute and charming, and I love him to bits for that, but holy moley!!!! He's kind of a handful to handle. And has given surprise bites to me (while I was medicating his ears), to our favorite vet, and to other dogs in my household. I have his nails trimmed at the vet's by two techs and with a muzzle, and it's inconvenient and expensive. And I have to keep him separated from my other dogs.
I wonder about health, too. The good thing about Chihuahuas is they generally don't have a lot of health problems, and on the average they live longer than other toy breeds. However, you might never get information about the health of your puppy's real ancestors and relatives.
Anyway, your contract certifies that he is purebred Maltese, Even if you are not sure you want to return him to the breeder, consider writing her soon anyway to question whether you "received what you contracted for." I would tell her you're going to have a DNA test done. If it confirms that he is a mix, a refund would be in order.
Edited to add: I understand that sometimes a potential mother dog will be sent to the potential sire's home for breeding. I suppose it's possible that some sneaky little non-Maltese male got involved somehow in such a triangle situation. Or maybe there was just one sire and he was a mix himself.
im
