Originally Posted by DOTTYMO

I calculate 10 3 inch wide stripes joined together should make a very long pieces about 205 inches which will be enough as you need extra to turn corners and to finish off. I did this with straight seams I have no idea of the way with correct diagonal.

Would it be easier as you have not done a binding before to use a gripes fabric with the colours that match. You would need to be sure 18inches. Cut across fabric so not many joins.