=HELP=iX6820 Print smaller than original files with colour stripes

I need to print a graphic pattern (the green boxes) on a 13" x 19" sheet for my school project but the iX6820 I just got ALWAYS print out the graphic smaller than the original file. There is also colour stripes on top of the image which looks like what a test print would do. Please see the attached file.

I tried to download the driver for mac and also set the paper to 13" x 19". Nothing worked so far. Since opening the box I haven't changed any of the settings. Anyone knows what's wrong with this printer?