Wrap A Scarf Around This Dilemma

i have found 1 truth very frustrating with this girls club. the girls
do not understand it is optional. i know they enjoy coming, but they
don't realize it's a privilege and totally optional. they seem to
think it's mandatory and no matter what we are doing they must do it.
although i want them to participate, i don't want them to be forced
like they seem to be now. crocheting a scarf is one craft that has
brought this to my attention. while i want them to have a chance to
finish, it's getting to a point of ridiculous. when i say i'll be
there after school so they can work on their scarf if they want to (i
don't take attendance and they don't need their membership cards-it is
a very informal gathering), every single girl shows up. there as 3
girls who will just sit trying to look like they are working if you
look in their direction, but they don't get it. there are a few who
try to secretly do homework but insist they are working on the scarf
if i try to address the situation. several girls should have been
done, but they all of a sudden only have about 3 rows completed. and
for the rest, they are either working slowly, distracting others
instead of working, or trying to have others 'help' them and pass it
off for their own work. it is frustrating me to no end. i am not sure
what to do now. i do not want to scrap the whole thing since i know
some girls really want to finish, but i also do not want to spend much
more time on it and having the girls who do not get it or who do not
want to finish become negative or resentful about their incorrect
belief that they have to do it. there has to be a solution and i am in
persuit of it.