QPrinter on QGraphicsScene Border Problem

How i can leave QPrinter border / margin ? my QGraphicsScene is exact A4...
the grey part is the paper & white is margin to write...
i wand fill exact the grey part on A4..

Now here .. QPrinter display a default border i suppose...

Code:

/* XSL-FO  -editor base widget   */
/* http://www.zvon.org/xxl/xslfoReference/Output/index.html 
<fo:simple-page-master margin-right="5pt" margin-left="5pt" margin-bottom="22pt" margin-top="22pt" page-width="21cm" page-height="29.7cm" master-name="first">
<fo:region-body/>
</fo:simple-page-master>
*/
void DisplayScene::MakefilePrintPdf()
{
    QString fileName = QFileDialog::getSaveFileName(this, "Export PDF",QString(setter.value("LastDir").toString()), "*.pdf");
    if (fileName.size() > 1) {
        QString UserlastDirOpen = fileName.left(fileName.lastIndexOf("/"))+"/";
        setter.setValue("LastDir",UserlastDirOpen);
        QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
        QPrinter printer(QPrinter::HighResolution);
        printer.setOutputFormat(QPrinter::PdfFormat);
            if (!fileName.endsWith(".pdf")) {
                         fileName = fileName+".pdf"; 
            }
        printer.setOutputFileName(fileName);
        printer.setPageSize ( QPrinter::A4 ); 
        QPainter painter(&printer);
        scene->render(&painter);   /* scene  QGraphicsScene   */
            if (is_file(fileName)) {
                QApplication::restoreOverrideCursor();
                /* disply pdf if exist! */
                OpenDesktop(QUrl(fileName));
            }
    }
    QApplication::restoreOverrideCursor();
}