You grin as you feel the tingling sensation center around your groin, mkaing you wonder how big Sandy will make you. You quickly position your boner so that it would grow between your massive breasts, essentially making you tittyfuck yourself. You grab your dick as the expansion begins, and embrace yourself for a wild ride.
You cock begins to grow longer, quickly reaching the foot long mark and thickens some. The growth quickly pauses, allowing you to rub your member some. The tingling begins again, this time making your dick grow faster than ever before. It quickly grows long enough to the point where you can see the tip over your breasts. You reach forward and grab it, pulling your penis towards you. You see that it's all veiny and muscley, with a rather red head.
You let go of your dick when it tingles some more, and stare in amazement at the growth. Your cock grows even longer and thicker, soon being long enough to brush the ceiling. You try to look around your dick, but it's just to wide. Smiling as the tingling sensation vanishes, you begin to rub your massive member with your tits as best as you can. The rubbing of sensitive skin on sensitive skin makes you almost moan in pleasure, but you hold it back so as not to alert your parents. You continue to rub, eventually making your dick drip pre-cum from the tip. Just about as you go in for the nut, you feel your balls tingle.
You reach down with both hands to feel your nuts. They're still the same size as your pre-transformation body, but you're sure you'll be lewdly rubbing more of your body soon enough.