Working-out Wrong?

It wasnt a pain, more like a "wow these got worked today" feeling. Even when we are working our back, I feel it so much in my bicep and not at all on my back. It's kind of annoying because I think my arms are going to get huge and my chest is going to be a fluffy bunny. I was doing the exact same motions as him, he even stopped to watch and make sure I was.

Is it possible that my arms are so underworked that they are feeling everything, as upposed to my chest/back.