Extend the Story - Add a Room

Nathaniel hurries into his room, cupping you close to his chest as to not drop you. From your position, you can now feel his muscles up close. Perhaps that was his intention, although you already know he outmatches you...in strength, at least. He kicks the door shut behind him and unfolds his hands, staring at you with an evil grin on his face.
"Now, finally, we can have some fun..."

You know you need to return to normal. He may be a dick, but he's a dick with at least some heart. You've seen such a heart out of before. Asking him outright may have some benefits, but is not guaranteed. BY the same token, if he shrunk you, he must have a way to grow you back. If you ask him about how he shrunk you directly, you could work from there to reverse it...however, the means of which he shrank you could be totally different from how he can grow you back.

You coyly ask him about how he shrunk you. The same thing could grow you back.