Black bed sheet, or black fabric from a fabric store (suck up your pride and step in their doors) is actually pretty cheap. Heck, Amazon.ca has a 60" x 102" polyester black tablecloth for CDN$ 10.99 (Amazon Prime eligible too) and that was just the first search result. Just don't put it RIGHT behind the screen, but behind your speakers and work with the projector angle a little bit for placement of the cloth (black cloth may need to be higher or lower than the screen itself once looking at from your seating position) and you should be golden.

Farewell - June 4, 2020