The floor. Why not?

You steady your breathing, and try not to flex your cock. Soon enough, a fast and far shooting stream rockets out from your stiff cock. It splatters against the hardwall, flecking off and running down into your carpet. You turn around a little, watching your stream soak your bed, splatter your TV, and get on your desk. You smile. It felt so good just go wherever you liked. After a little bit, the stream loses steam, and reduces to a dribble. There. You take the dregs of your pee and stroke up and down with it. Pre swiftly mixed in, making your member insanely slick.
You let go before you lose yourself. You crouch down and grab the book. With a look of hedonistic glee, you flip to the spell you found that first day. There were varying levels, so you decide to slowly ramp up to ridiculousness and start out small. You recite the words. As soon as the last syllable leaves your lips, your balls rumble. The bubbling sensation radiates bliss, so intense that you drop to your knees. Through heavy lidded eyes you look down at your junk. Your balls were egg-sized, held in a warm pudgy sac. The bubbling was less intense, but your junk still glowed with pleasure. You take your cock in your hand and notice that your urethra was now wider. The implications made the tip bead with a large glob of pre. You take your shaking member in your hand, and pump. Greased up by your pre and piss, your hand slides effortlessly up and down. You groan at how good it feels, slowly standing up on shaking knees and walking over to your bed, never stopping your hand. It took no time at all to reach mind-mushing climax. You feel the bliss well up in your balls, and wrack your body as it spews from your slit onto your sheets. After a half minute of shooting steaming thick ropes, the pleasure finally wanes. You chuckle and let your head drop. Your balls haven't shrunk at all, but your cock is still twitching in your hand. Your eyes go wide when you look up. From the tip of your cock, across your bed, to the ball, your sheets and quilt were swamped in your goo. It was absorbing a little, but mainly stayed steaming in a clump on the top. You smile back down at your cock. The spell removed your refractory periods, so she was already to go again. You look to your door...