OpenCV camera calibration - Intrinsic matrix values are off
Cx and Cy are the coordinates (in pixels) of the principal point in your image. Usually a good approximation is (image_width/2, image_height/2).
An average reprojection error of 0.08 pixel seems quite good.
I used OpenCV's camera calibration function for calibrating my camera. I captured around 50 images with different angles and pattern near image borders. 
Cx and Cy value in intrinsic matrix is around 300 px off. Is it alright? My average reprojection error is around 0.08 though.