Still reading your advice. Thanks.
We use a variety of point-and-shoot digital cameras at work, some of which "appear" to display their files at a higher res. hence my confusion. Thanks Jim for the explanation, all makes sense now.
I've attached a gif of the full frame. Obviously it's not much use other than to show composition.
I still have the concern that as I shot at f2.8, thereby using more of the lens, could the CA be a characteristic of the lens? As JimC has said, the CA is definitely worse on the poles nearer to the camera, ie the edge of frame.