According to Fuji,
Image area: Approx. 73×95 mm (2.8" x 3.7")
Frame: Approx. 85×108 mm (3.3" x 4.25")
If that's what you're getting, all is ok.
Ok - I have the EE100 Special, but have not used it yet. However, I believe you should be able to use the entire image area except for the white frame, of course.
My reasoning is based on another camera: the Polaroid Super Shooter. In the actual viewfinder of that camera, there is a mask that shows a square image area. However, if you insert a Fuji pack cartridge into the camera, the upper right edge of the cartridge presses on a small lever and that causes the viewfinder mask to change to a rectangle. I can can also move this with my finger and cause the same thing to happen. I suspect there are square-format cartridges that don't press the lever.
I was not able to find such a lever in my EE100 Special - but that makes sense, since there's no moving viewfinder mask in that camera - the lines are etched, as you noted.
However - the important thing to note is all this square vs. rectangular imaging is in the viewfinder only - there is nothing that moves to cover or uncover the film. That is, when you insert the cartridge, whatever the image area is on that film should be what gets exposed. I cannot explain why you'd be getting a square image, so measure and check the dimensions I posted above.
Experiment by keeping the back open and putting a thin sheet of paper were the film would be. Go into a darkened room and point the camera at a brighter room or point it outside. When the shutter trips, the entire paper should be exposed.
As an aside, it took me a while to discover that the camera will do long exposures up to 10 seconds, but you have to hold the release until you hear the shutter close. Also, in 3000ER range, the aperture is always wide open - so you can make handheld shots indoors in very dim light with FP3000B.
