I am not certain of the species, other than it is not Ancistrus (Bristlenose). If it is a common pleco (Hypostomus plecostomus) it will attain somewhere between 12 and 20 inches. It requires at minimum a 4-foot long tank, though larger would be preferable. It is a huge waste factory. Now is the time to re-home/return if this is not in the near future, as this is less stress for the fish than later.