You mean how the foggy outer rectangle doesn't line up with the main image rectangle? What's happening (probably) is that you shot a very backlit or flarey scene, or overexposed a bit. Flare inside the camera does not necessarily come from the exit pupil of the lens and therefore it can pass through the film gate at a different angle, resulting in an offset and/or larger region of flare on the film compared to the focused image. Think of the sun being just out of frame, the lens will form an image of the sun on the inside side of the camera or somewhere in the lens barrel. That sun-image is maybe a thousand times brighter than the image you care about, which results in a mass of light bouncing around within the camera and onto your film, and you get veiling glare.

When you scan this, you'll probably find that all the blacks are a bit washed out from the flare. Setting your blackpoint higher in the scan will clean it up a bit.

To see a similar effect, shoot an image with very shallow DOF, which will mean you have a larger exit pupil of the lens. You'll therefore see that the edges of the image become blurry, i.e. the film-gate casts a penumbra instead of a clean-edged shadow.