If that curtain fabric is a quality, weave, content good for quilt backs or backing for wall hangings, I would use it like that rather than toss it out and buy something else.
My stash is too large cuz I'm a fabricoholic and cannot use the fabric I have in multiple lifetimes.
My MIL still quilts and she's 90. She always bought only what she would use, never had a 'stash'. She saw mine and I think the poor woman was gonna faint away, or think I've been spending too much of her son's $, LOL. But at the same time, a smile came over her face and she's been so supportive ever since. HA.