inkscape - Decreasing the page size when saving to PDF

I created an SVG image in InkScpae. It is 1328 pixels wide.

Then I did "Save as PDF". The resulting PDF was 15 inch wide.

I need the PDF to be in the width of an A4 paper - about 8 inch.

I tried to play with the DPI setting, both while saving the PDF and in "File -> InkScape settings". I increased the DPI from 90 to 200 and to 300, but it did not change anything - the PDF is still too wide.

What can I do?