Sometimes lower end cameras do this lens board thing. It is just on account of sloppy tolerances in design and manufacture. It is minor; it amounts to a millimeter or two of lateral shift if it happens between the time you compose and when you take the shot. Every old metal Calumet or Graphic View I have used has done it a little bit. The board won't shift when the photo is being made unless you move it by accident with the cable release. If you want to be doubly sure, use some gaffer tape or masking tape to hold the board in place. I never had a problem with my own GV, or any of the borrowed Calumets I used, though.
Another option might be to install a thin strip of material on the left or right edge of the lens board hole; it will take up the gap. I'd probably do it with slices from a piece of construction paper or a Pee Chee folder, and use tightly-applied Scotch tape to stick it on. You could use metal shim stock if you want to make it a more "professional" rig job.
There should be a slot near the edge of the back from which you insert the film holder. A tab on the film holders fits into that slot. The film ends up where the ground glass was (hopefully ), so everything ends up just like you saw it on the ground glass, even though the ground glass moves before taking the pic.