Nice one Jon 🙂
Three options exist.
1. Square the plane.
2. Adjust the blade til it’s square to the shooting board runway.
3. Invest in another plane. I’d suggest a #5/#05.
It’s not too unusual for a plane’s sides to wear and drift from true, but I’ve encountered this aspect more with Stanley than Record planes and suspect it could also relate to casting quality. Another adjustment you could make concerning your shooting board would be to plane a channel in the outer edge of the runway and inlay a brass or nylon strip (Not steel or iron as it would wear on the side of the plane) to compensate for the existing inaccuracy, but this would potentially leave you unable to use other planes with the shooting board.