HappyHolidays! is designed to print cards onto paper which is the same size or larger than the intended card size.  To print 4"x6" cards onto 4"x6" photo paper, your printer must support full borderless printing so that the paper size reported back to the program from the print driver specifies that the size is large enough to accept a full 4"x6" image.  Be sure to use Page Setup to pick the correct 4x6 borderless page size.

When printing to paper which is the exact size as the desired output, please be sure to disable the printing of cutting guides by visiting the HappyHolidays! Preferences and turning off the "Print cutting guide lines" option.