Dear Anon,
I applaud your quick thinking and agree that logically that would have worked, if a shrinking potion actually reduced the size of something rather than compressed the afflicted area and used an ongoing magical effect to 'trick' the mass into behaving as if it were the appropriate amount. Always read the warning labels and do not use any potion with which you are not intimately familiar without a practiced potioneer on standby.
Good intention, terrible execution. Better luck next time.
Penned by,
HRH Celestia
To my faithful student, Twilight Sparkle,
Not every idea is a good one and even a slight miscalculation or misunderstanding on the part of a spellcaster can turn a good idea into a bad idea. As you well know.
I am pleased to hear miss Trixie will be well, and in the future perhaps research her stage magic a bit more thoroughly. Casting a spell to achieve an effect and making ponies think you cast a spell when you didn't are very different, and are difficult in their own ways.
Your loving mentor,
Princess CelestiaPS. I do hope you realize this was a case of misunderstanding a magical effect rather than a problem inherent in, say, one's origin.