One of the hardest things to do is to get any windows application to print to a DOT Matrix printer. It is even more difficult when you want to print to a short form. When Bill Gates wrote windows he specifically wrote it for Laser printers (that only print standard paper sizes).

It's unfortunate that you bought a new printer, likely this was not required. Assuming that you only use the printer in question to print the 7" forms set the printers internal memory to 7" paper length.