take a piece of waxedpaper and tape it on the film gate / place where your film would sit to be exposed.
open your shutter up / bulb, and get a loup and focus your camera and see if with the stretched tight
waxed paper the image is sharp from edge to edge. if it isn't ... your lens is off-kilter
if it is sharp from edge to edge it might be something like a roller or pressure plate not being right ..
and you need to have it straightened, unless, you want to use that affect as an effect and have it part of your signature
good luck !