Depending if the printer connected to the server, or to an other PC running device controller, you have to edit application.xml or controller.xml:
You can find the same section in both application.xml and controller.xml files:
<!-- WINDOWS PRINTING -->
<property name="offset" value="0" />
<property name="margin" value="8" />
<property name="paper" value="0,0,0,0" />
The „paper” parameter defines the paper size of the Windows printer in pixels. If all values are „0”, the system is using auto detection.
In case the Windows driver not allows to set paper size, or the printing size is still incorrect even after setting the right size, you can set the values manually:
The meaning of the four values are:: x,y,width,height
It might be necessary to do some tests until you find the right values. Probably setting „5,5,566,800” or „0,0,576,800” will be OK in case of your 3” printer.