Many people panic on their first interview and fail, and if you show any potential they'll let you interview again. I bombed my first one and they told me that I'd be eligible to interview again in 18 months and I should call them then, and they actually called me in 12 months and set up another interview.

Don't worry about the courage, just apply. If you fail... well, many many people (and many many Googlers) also failed their first Google interview, it's not much of a reflection on you.