You have to either select existing printer form with the size that fits your requirements or create custom one as shown in How to add/delete custom printer forms under Windows NT/2K/XP FAQ #21202

>I'm getting some additional new grey hair - and I know I've solved this before.
>
>I'm trying to print checks on 7" stock on an OKIdata 590 printer.
>I've followed the Okidata instructions and a test sheet (lines of x's) prepared in WordPad prints for a 7" page just fine.
>
>I prepared a simple list of inventory items, with the OKI as the default driver. It printed as if for a page just short of 12" (text + page break).
>This is very close to A4 paper size....
>
>The checks print as if the page as that same 11.75 inch stock.
>
>
>BTW - I am using the Epson 2550 printer driver, as recommend by Okidata.
>I'll check tomorrow to be sure that the printer is set to Epson 2550 emulation, not IBM emulation.
>