If you look at the edge characters describing the film type and frame numbers, they are nice and vivid while the photographic negatives themselves are very thin. That indicates that the lab probably processed the film well, and your negs were extremely under exposed as others have said.
Either the light meter was giving bad information, though from your description you'd still be in the ballpark, or there's an issue with your camera or with your use of the camera. You sound like you have a good idea of what you should be doing, so I'm edging towards the idea that it's the camera at fault.