Get real with the friend right away. Ask if she would accept a lap robe instead if you really can't afford the big quilt costs.
We do tend to forget to engage brain before starting mouth.
I'm still cursing because of the one I'm trying to work on now, I forgot that I had made a template for a block and then didn't like it, made another one. But still cut with both of them since I didn't MEASURE them before hand. Now I have enough of each size for a lap robe, but not one big quilt. And I'd promised it to my sister for Valentines' Day. I'm beginning to hate that pattern, used to love it and probably will again. Someday.