All those wonderful comments - thank you all so much.
One more silly question: Did you sew yours to fit INSIDE the window casing or OUTSIDE the window casing so it slides up and down the wall?
I would think that if it's inside the dimensions have to be right on, whereas outside gives a little room for a fudge factor.
Oh - and not kids in our house (I'm allergic - lol) But I did catch one of my cats getting tangled when he played with a pull string, so the same rules apply.