Digital BW, The Print

Hello,  I just received and set up my 1280 which I will be using for 
B&W but decided to run a few test prints with the color inks first.  
The color is nice but when testing on 4x6 paper (landscape setting), 
the printed image is not centered:  the image size to be printed was 
4x6; the paper size, 4x6; with or without the "borders" box checked, 
they all are the same:  lead edge, 6mm border; bottom edge, 2mm 
border; trailing edge, 3mm border; top edge, no border, hence, printed 
image size, 3 7/8  x 5 5/8, +/-.  I did print the same 4x6 image on 
8.5x11 and it did print a 4x6 image but not perfectly centered when I 
had it set up to do so.  Any clues?  I hope this printer didn't 
receive too many bumps with UPS on trhe way here.  Any help greatly 
appreciated.