There is an intense feeling inside you, a swelling of energy that feels like a cross between a sugar rush and an electric shock. The energy pulses outward into your hooves and tail, making your mane stand on end and your cheeks flush. You suddenly feel quite light-headed, and take in a deep breath. A breath that lasts much longer than you realize.There is a light thud against your scalp, but whatever you've hit quickly gives way with a creak and a snap, feeling no harder than a piece of styrofoam.
Finally, the bright flare of light passes from your eyes, and you can see the bright blue sky again. Wait... The bright blue sky? You were inside the library minutes ago!
"It works! Sweet Celestia it works!" you hear a tiny voice, Twilight's, below you. You look down and see the leafy tops of the library tree, then it hits you. From your sitting position, you're easily head and shoulders above the library, literally! A quick glance around your surroundings proves that you're taller than most of the buildings in Ponyville!
"Peachie! It worked perfectly!" Twilight cheers again. You try to adjust your legs to see her better, but you end up pushing your soft sole up against her, smooshing her gently against the wall. She lets out a pained squeak, and you quickly withdraw. You readjust your self, putting your massive legs on either side of Twilight.
"There," you say, "Not squishing you, am I?"
Twilight doesn't respond. You glance down at her, and she seems to be staring at something, but from your angle you can't see what it is. In fact, from above it seems she's looking right between your... Oh my. You just unwittingly spread your massive legs to her, revealing your womanhood in full. You very quickly bring your knees up to your chest to keep her from staring any longer, blushing heavily.
"I, I think maybe I'll just step outside," you say, nervously. Then you step out and over the library, taking special care not to knock your knees on any nearby buildings or, Celestia forbid, step on a fellow pony. Twilight follows you out, opting to use the front door instead. A small crowd of ponies is beginning to gather around you, making you feel quite nervous at how they might be staring at you.
"Well!" Twilight says, still blushing from before, " I guess we can call that spell a smashing success, right Peachy?"
You nod slowly, stirring up a small breeze, "Yes. All according to plan. Now let's shrink me back down so we can keep testing those spells of yours."
"Um, well you see, that's the thing," Twilight says.
You cut her off, saying exactly what you know she's going to, "You can't change me back."
"Not immediately," Twilight says, feeling quite bashful, she adds in, "But it can be done! You remember that circle we had drawn on the floor? Well, as I mentioned, it uses complex runes and geometries to perform the incantation, but it was smeared by your hooves when you grew. Even with magic it'll take me the better part of a day to redraw. I'm so earnestly sorry."
You give a warm smile, sensing honesty in Twilight's apology, "I suppose it's fine, Twilight. No harm done, and I DID volunteer."
"Is there anything I could do for you to make this enlargement comfortable? I mean, that size must take some getting used to. Perhaps you'd need some nutrition to supplement your large belly? Or maybe the spell has caused some skin irritation, the book did mention that might happen."
"Well," You say, "I...