The Gestalt Prayer can be found in a number of sources, including this one from the Bantam Books edition of "Gestalt Therapy Verbatim"...
I do my thing and you do your thing.
I am not in this world to live up to your expectations
You are you, and I am I,
And if by chance, we find each other, it's beautiful.
If not, it can't be helped.
In the more recent Gestalt Journal edition of this book, there is an excellent introduction by Michael Vinvent Miller, which puts the book and the Gestalt Prayer in the context of the times - the '6o's. Miller notes that much of what is in the book and prayer are as much about the era as about Gestalt therapy. Remember this was a time of the quick sound bite to encapsulate a movement.
There has been a recent heated debate on the AAGT email group about this very topic, the Gestalt Prayer, along with discussion about the spontaneity or rudeness (or both) of Perls barking on his hands and knees at Maslow when he presented at Esalen.
Personally I prefer this quote from Perls...
"Friend, don't be a perfectionist. Perfectionism is a curse and a strain. For you tremble lest you miss the bulls-eye. You are perfect if you let be.
Friend don't be afraid of mistakes. Mistakes are not sins. Mistakes are ways of doing something different, perhaps creatively new.
Friend don't be sorry for your mistakes. be glad for them. You had the courage to give something of yourself.
It takes years to be centered; it takes more years to understand and be NOW."
Perls - In and Out the Garbage Pail