And that is a hard but valuable lesson to learn.
I don't think thats a gibbiceps, they usually have the leopard-spot pattern. Most likely any of several species sold as "common plecos", most of which will get from 12-24" and are absolute waste machines after they hit about 6-8". Within a day after gravel vac'ing my old tank, I would have piles of pleco poo in the corner from my 10" guy, it was crazy.