Yes I know all about the anatomy. I've been doing PC exercises for three years, so I think I know what I'm talking about. That "lump" is your internal penis. It's bigger now because you have better circulation because of PC exercises. It is not the PC muscle itself. If you press that lump with your thumb you should be able to feel your urethra. If it were your PC muscle it wouldn't automatically get hard when you are erect because it is a voluntary muscle. You have to flex it, it does not flex on its own. It gets hard from the bloodflow during an erection because it is the inner penis.