Defining "just right"

How do you know when you've prepared for something, as the littlest bear would say, "just right?" When are you exerting too much effort, or not enough?

I had to play piano for an audition last week. For the past couple of years, the only piano playing I've done is to pound out my notes for various singing performances. I hadn't played any of the pieces I used to play semi-well.

The day I found out about the audition, I decided to work on a Brahms waltz. I practiced. Then the script arrived, and it looked like I'd have to play and talk at the same time. I practiced. And practiced.

The audition coincided with the worst December snowstorm here in years. That morning, I watched the weather reports. I practiced. And practiced. I left an hour and a half early for the suburban studio. Fortunately, hardly anyone was on the roads which had just been cleared, and I got there in record time.

Upon arrival, I learned:
1) Playing and talking were separate.
2) I only needed to play a few chords, not a whole piece.
3) Tho I'd pretty much memorized all 3 paragraphs of copy, they only wanted me to do the first two (the last was the longest, and rather technical).
4) Many people had cancelled their auditions and were rescheduling for another day.

Could I have allocated my time more effectively? Do you think it's better to be too prepared?

Will I get the part? Stay tuned...