We too love California Grill! We've been twice. The first time was phenomenal. The second wasn't as great of an experience, but we still enjoyed our meal very much.
I would never hesitate to order what you want at any restaurant. As many have already said, it's your meal. You are not there to please the server. They're there to make your experience enjoyable.
Now, as for the size of the flatbread - I personally don't think it would be quite enough for dinner. They aren't tiny, but they're not really entree size either. If you don't have a big appetite, or just don't eat much in a single sitting, you might be satisfied. But you won't be "full", I wouldn't think.
In any event, I think you'll really enjoy the view and atmosphere. The food is excellent, no matter what you order, and the service is great too. Have a great time!