You never stop feeling nervous when something important is on the line.

Ex-Googler here. Working at Google is very different than making a presentation representing your own idea. At a big company, assuming a collaborative culture, your teammates are rooting for you to do well and you don't go into a meeting expecting that to be the last word if they don't like your idea. OP had already quit his job, staked his reputation/ego on his demo, and had to speak for himself in a tough room, so I think it's reasonable to feel some level of nervousness.