Let us know if you are on OS X or on Windows.
If OS X, did you set Page Size only in Print Tool? Or in both Print Tool and also in QTR.
If in both, did you make certain that both the Print Tool printer and the QTR printer are the same and therefore the page setups the same?
Did this work previously ok, but suddenly not.
Did you upgrade anything between when it did work and when it did not.
Have you ever been able to center an image on 13x19 whether with QTR or the standard Epson driver?