QTR-Quadtone RIP

Hi,

I am printing B&W folded greetings cards to A5 from A4 paper.   For
example, I size a portrait image 180mm wide by 246 mm high and, using
`canvas size' in PS CS3 add a 5% white border to the bottom of the
image.  I then increase the size for equal white borders on to A5
sized paper.

I then increase the canvas size by 100% to the left for text relating
to the image.

I then rotate the paper to print on QTR.

Although at A4 size  this  does not fit the A4 setting in QTR and,
sizing to fit leads to a 96% resizing.

When printed to fit, and after folding, the image margin on the left
of the A5 card is narrower than the margin on the right.  Does anyone
know why and what I should do?

Colin