I'm at 335lbs right now, and Have had a Carbon road bike for about a year with no issues at all with the frame itself. There's a few others around the same weight as us too, and they haven't had any problems either. I'm more worried about busting wheel spokes than anything on my bike, and that has yet to happen. Hope this helps!
And no need to feel embarrassed about going into bike shops. Be proud that you are taking the initiative to get exercise. All but 1 shop I've visited have been very supportive and helpful.