Hi,
The HP Deskjet 3050 do not upport custom paper size and therefore a such will not be listed by the print driver, it do not offer such functionality.
The steps described are intended for later HP printer models, for 'HP inkjet printers introduced after February 2013' only, as clearly described by the document:
https://support.hp.com/us-en/document/c03890386
The HP Deskjet 3050 (J610) was introduced in July 2011 and do not support custom paper sizes on Windows::
http://h71016.www7.hp.com/html/pdfs/dj3050j610a.pdf
Regards,
Shlomi