Refraction Error in Viewfinder after disassembling

I disassebmled my Nikon D60 like explained. But now when I disassemble the whole part with the Flash on it and the black cover with the objective on the camera, I have to push the black cover with the Flash part a little bit down to click into place the black cover with the objective. But if I do so, I get a little preasure on the Roof prism and therefore I get a refraction error in the middle of the viewfinder. I can see a small part double. Only in the viewfinder and not on the Picture. If I release the preasure by pulling the frontcover away the view will be fine. Someone had the same problem ? Thanks