Reading this, I remembered my own way of getting rid of that stressed shaking before a performance, be it guitar playing or public speaking.
I would always find a way to shake that stress off just before I start my performance. In public speech contests, I would have my piece written down on a sheet of paper, which I would quickly crumble and throw away just as I'm about to start. When playing the guitar, I would simply strike that first chord and project my stress into it, so that once I've started, the stress has been thrown away at the same time.
No amount of preparation would ever help me relax. This stress-throwing at the start of the performance is what has helped me best so far. It's all about finding the way of throwing it away.

P.S. Even though you felt like a cucumber, at least you didn't have to wear that awful green costume this time ^^ Congrats on your first solo performance!