Is it canvas you're printing on??
Application of the protective varnish is usually where the Costanza Effect is most pronounced, but shrinkage can/does occur right out of the printer too. Canvas is "cloth" which is pliable and stretches a bit. Shrinkage occurs along the length of the print.
I'm not sure about the 11880 driver, but the 9900 allows designation of "canvas" under fine art media selections on the printer. This often resolves much of the shrinkage issue.
It's not too difficult to figure out the percentage of shrinkage to compensate for in PS, or use a printer utility like Qimage Ultimate, which allows you to enter that percentage into the program when printing on canvas.
ken