How important is it to get the wall dead centre? I've got 600mm width by about 600 deep in clay but there's a bit of a banana shape to it that I only eally noticed after the concrete had gone in TBH and the wall gets to about 7cm from the edge in the middle, It's single storey & fairly lightwight - is BCO likely to have problems with it / what do you actually do to remedy the situation?