The pattern gives the size as:
Length: approx 150 cm [59’’]
Width: approx 25 cm [9 3/4’’]
It looks as though you can continue the pattern repeat of rows 1-38 until you get the width that you would like. You might want to cast on slightly more sts in order to keep the proportions on the scarf. You would then adjust the position of your marker threads. The exact number of sts between markers won't be critical although it will start to affect the size of the flounces.
It's really a very good looking scarf. I think that once you start it, you'll be able to judge how wide you want it to be.
(Please edit you post to decrease the font size so that it will be easier to read.)