Never never never let the "rules" rule! I've had cameras with viewfinders that weren't seeing exactly what the film did. I had to include a little more in the frame of the viewfinder then print the image I actually saw when I took it. Even so the act of pointing the camera and choosing the distance is essentially cropping albeit in camera.
When Ansel Adams had a fire in the Yosemite studio he had to put all the glass plates in the bath tub. The famous Half Dome plate lost part of the image so he had to crop the image in printing. He didn't throw it away but used what he had. And that's good, it is a great photograph!