I've just looked at your photo. Yes, it is as I suspected - the arm mounting slot, at 300mm, is too far from the platter centre. The arm is hard up against the bedplate (nearest to the platter spindle).

You need to reposition the bedplate a little closer to the platter centre, so you can achieve the correct overhang according to Stevenson's geometry; that is, with null-points at 60.3mm and 117mm.