Give Megan a late growth spurt, starting today and taking course over the summer so as not to arouse suspicion.

You consider for a moment the possibilities of this stone, and the possibility that undoing things might get complicated. Considering that, you decide to start of with a more subtle approach. You can always reveal the wishing stone to Megan later, right?

You think carefully about how to word your wish, and once you've got it you grasp the stone in your and and utter the words:

"I wish that when Megan wakes up this morning, she'll notice she's an inch taller and started a late growth spurt, which will cause her to steadily grow at a rate of an inch every day for the next week."

As you finish speaking, you half expect to feel some sort of magical wave of energy wash over you, and you're almost disappointed when all you get is a slight pulse of warmth from the stone in your hand. It makes sense though, you reason, considering the wish had no direct effect on you like your previous 'wishes' had.

In any case, you know that Megan likes to sleep in any chance she gets, "My coach says it helps your body recover, so really I'm helping my basketball career" she always says when you give her shit about oversleeping. In any case, while the two of you made plans to hangout together today you know you probably won't hear from her for a bit til she wakes up.

Eager to see how your unsuspecting best friend will react to her new growth, you quickly get ready for the day. Checking the clock you see it's still only 8:30, and you probably still have quite a while before she wakes up.