Rewrite this so it sounds like something you would say and then practice saying it so you will be ready the next time someone puts you on the spot. Sorry your friend has sucked you into a project you won't enjoy because you were trying to be nice.
"Quilting is my creative outlet and I really need to follow my muse and make things that catch my interest at that moment so I have trouble making projects that others have planned for me and I didn't choose. When I do that it feels like work to me and takes the joy out of my hobby!"