Establish some moral boundaries first, then cut loose

Truthfully, there was a lot you wanted to do, obviously. The possibilities were endless, but there was only one thing that was really stopping you: Your own moral compass. Megan is your friend after all. Even if you were starting to suspect that she may harbor some of the same desires as you, it wouldn't hurt to make 100% sure that she was on board.

"I wish that any further wishes I make involving Megan will be nullified if Megan would not also want them to happen." You pause for a moment, then add, "All ongoing changes will also cease the moment she feels uncomfortable."

Just then a tingle runs through your fingers, seeming to come from the wishing stone. You take it as a sign that the wish worked, and you smile to yourself. There. Now you can do whatever you want without any guilt!

You hesitate, nervously considering your options. Now that your inhibitions are gone, you can't help but want to turn things up a notch. Your heart is pounding in your chest, and your fingers tremble as you barely clutch the stone. Only a single inch per day just isn't gonna cut it, you decide.

"I... I wish that Megan's rate of growth will increase to two inches per day." You barely manage to utter, nearly fumbling the words as they left your lips, "And that I will also shrink at the same rate."

This time your whole body tingles as it did before, a thrill rushing up an down your spine as it does. Knowing that it meant that your wish had been granted, your cock immediately springs to life in your tightening pajama pants. You gently stroke yourself through the loose fabric, getting more and more excited. You can't help yourself.

"I... I wish that Megan's breasts will grow larger."

It was a selfish wish, you knew, but you couldn't help it. Your lizard brain demanded it, even. But you had heard her complain about her lack of a bust in the past anyway. You were doing her a favor, really. Besides, if she didn't want it, then the wish just wouldn't happen, right?

More tingles in your fingers, letting you know that Megan did, in fact, want it and that the wish would, in fact, be granted. Your hand plunges down the front of your waistband and you pull your cock out, stroking it as fast as you can.

"...And her butt..." You add, still stroking yourself, still clutching the wishing stone, "...Her thighs, her hips... I wish they'll grow bigger too. Curvier. Thicker and fuller and... Ugh!"

The wishing stone falls out of your hand, but not before making your fingers tingle one last time. It falls off the edge of the bad and patters to the floor. The mental image of a taller Megan consumes you in your passion, smiling down at you over the swell of a truly imposing bosom. You cum in record time, thoroughly soiling your bedsheets, and sleep finds you not long after that.