Another thing to try is to set standard paper name.
From VStudio it is printed with the correct size, so what size do you set in the print dialog?
Here are possible values for paper parameter (in the first column, the second value is the corresponding constant in the Windows API):
{ "letter" , DMPAPER_LETTER },
{ "letter small" , DMPAPER_LETTERSMALL },
{ "tabloid" , DMPAPER_TABLOID },
{ "ledger" , DMPAPER_LEDGER },
{ "legal" , DMPAPER_LEGAL },
{ "statement" , DMPAPER_STATEMENT },
{ "executive" , DMPAPER_EXECUTIVE },
{ "a2" , DMPAPER_A2 },
{ "a3" , DMPAPER_A3 },
{ "a4" , DMPAPER_A4 },
{ "a4 extra" , DMPAPER_A4_EXTRA },
{ "a4 plus" , DMPAPER_A4_PLUS },
{ "a4 small" , DMPAPER_A4SMALL },
{ "a5" , DMPAPER_A5 },
{ "a6" , DMPAPER_A6 },
{ "b4" , DMPAPER_B4 },
{ "b4 (iso)" , DMPAPER_ISO_B4 },
{ "b4 (jis)" , DMPAPER_B4 },
{ "b5" , DMPAPER_B5 },
{ "b5 (jis)" , DMPAPER_B5 },
{ "folio" , DMPAPER_FOLIO },
{ "quarto" , DMPAPER_QUARTO },
{ "9 x 11" , DMPAPER_9X11 },
{ "9x11" , DMPAPER_9X11 },
{ "10 x 11" , DMPAPER_10X11 },
{ "10x11" , DMPAPER_10X11 },
{ "12 x 11" , DMPAPER_12X11 },
{ "12x11" , DMPAPER_12X11 },
{ "15 x 11" , DMPAPER_15X11 },
{ "15x11" , DMPAPER_15X11 },
{ "10 x 14" , DMPAPER_10X14 },
{ "10x14" , DMPAPER_10X14 },
{ "11 x 17" , DMPAPER_11X17 },
{ "11x17" , DMPAPER_11X17 },
{ "note" , DMPAPER_NOTE },
{ "envelope" , DMPAPER_ENV_ITALY },
{ "envelope monarch" , DMPAPER_ENV_MONARCH },
{ "monarch" , DMPAPER_ENV_MONARCH },
{ "envelope #9" , DMPAPER_ENV_9 },
{ "envelope #10" , DMPAPER_ENV_10 },
{ "envelope #11" , DMPAPER_ENV_11 },
{ "envelope #12" , DMPAPER_ENV_12 },
{ "envelope #14" , DMPAPER_ENV_14 },
{ "envelope dl" , DMPAPER_ENV_DL },
{ "envelope b4" , DMPAPER_ENV_B4 },
{ "envelope b5" , DMPAPER_ENV_B5 },
{ "envelope b6" , DMPAPER_ENV_B6 },
{ "envelope c5" , DMPAPER_ENV_C5 },
{ "envelope c3" , DMPAPER_ENV_C3 },
{ "envelope c4" , DMPAPER_ENV_C4 },
{ "envelope c6" , DMPAPER_ENV_C6 },
{ "envelope c65" , DMPAPER_ENV_C65 },
{ "envelope invite" , DMPAPER_ENV_INVITE },
{ "c" , DMPAPER_CSHEET },
{ "d" , DMPAPER_DSHEET },
{ "e" , DMPAPER_ESHEET },
{ "japanese postcard" , DMPAPER_JAPANESE_POSTCARD },
{ "fanfold" , DMPAPER_FANFOLD_US },
{ "letter extra" , DMPAPER_LETTER_EXTRA },
{ "legal extra" , DMPAPER_LEGAL_EXTRA },
{ "tabloid extra" , DMPAPER_TABLOID_EXTRA }