yeah petco will return it, if you are exchanging and it's alive they will likely even return with out a receipt, I returned a bad power head there once with out a reciept and they gave me a new one, it was used and retail was like 70 bucks. Didn't give me too much hassle.
Petco generally only carries common plecos, so return him.
They sometimes have rubber nose in stock there. They stay smaller.