I have been thinking about this, and am going to ask what may seem a really dumb question: Do you actually own a pitbull? Maybe that would be the first thing to determine for sure.

I am posting a link to prove my point.
Pet Pitbull - Find the Pit Bull

My brother bought a 'mastiff' X which is now fully grown and looks almost exactly like a fox terrier. People do get it wrong all of the time and you may want to consider if what you have is indeed a pitbull, and not a mix of staffy or mastiff or anything really. Do you have papers with it?
I like that link. It really does show how similar some of the breeds can look. I got it right first time, BUT that's with many many years of vet nursing under my belt. I bet a lot of people would take a few guesses to get it right.