You can do it by cutting and folding a sheet of clear acetate or similar from a net like this: https://wp.optics.arizona.edu/oscoutreach/wp-content/uploads...

Or you could cut the four sides separately and just sellotape them together.

edit: not much help without measurements sorry - try this: https://www.holeinthewallgang.org/Customer-Content/www/CMS/f...

The required angles appear to be 54 or 126 degrees: https://data.formsbank.com/pdf_docs_html/304/3049/304991/pag...