Eclipse error

There was a partial solar eclipse this evening. I quickly built a box with a lens and a paper back with which I thought we'd be able to carefully study the phenomenon. Unfortunately, it did not seem to reveal the changing shape (see box and back image above). We COULD see the eclipse when we held up two layers of welding goggles in front of our eyes, so I know that the images in my makeshift camera obscura were wrong. Maybe it was a factor of the lens aperture which made the non circular sun circular? The internet said to use a pinhole. I have lots of pinhole stuff around, so I should have done that.