[That's an understandable anxiety, in some senses...]

I'd not take these circumstances brought on by the mirrors as a sign of your personal ability nor any lack thereof. I merely mean to say... I believe you're capable of more than you've claimed to be.

[The magic of this world is incredible like that. He's seen so many remarkable things both from others and himself, even though he never would have believed in sorcery of any kind back home.]

If you prefer not to attempt any further magic for the time being, I'd only suggest you memorize your experiences from your new perspective, at least in terms of your height. I've found such visualization helpful when attempting my own voluntary transformations.