omark,
What Stophel is simply telling you is that the buttplate is not too narrow, the butt is too wide.
Any good precarve should have a little extra meat to allow for shaping and carving.
Is the stock inlet for the return - tang - on the plate? If it is, then plate location has been firmly established for you...unless you do as Curt L did and switch to a plate with a wider return. If the return is not inlet, do as Stophel says and push it right to cover the box dovetail and give you that castoff then shape your stock to it.
Hope that helps, J.D.K.