Your printer has margins that it can not print on. To view the printable area, create a layout with thick lines vertical and horizontal. Print with optional margins set to minimum. Margin settings are not always available in Print Setup, it depends on the Printer driver.
The dotted lines in Layout Mode show the printable area for the last used Print Setup you used.
Margins can be set in Layout Setup...
If you set top and bottom margins of a bit more than half an inch, at the least, you can set up a layout (where you don't add any white space for margins), that will print the same on almost all plain paper printers. (Most plain paper printers can print very close to the top edge and close to half an inch from the bottom edge.)