I'm thinking that its light leakage too. But I thought that I did pretty well with the lid. If it was an aperture or exposure time issue, I would think that I would get an image, just badly over/underexposed...not completely blown out.
As I'm writing this, I'm starting to wonder about the seal around the aluminum sheet used for the aperture....hmmm
The camera is made out of the larger size oatmeal cylinder, so distance to paper is about 5" or about 12,5 cm.
I'll try some of your suggestions and see what happens.