Hes looking really good!
I've made a banner of my own once. I used a piece of an old shirt, cotton. I cut the piece out the size that I wanted + a little more in the top*, and then covered it (not soaked, but almost) in Pva glue.
*I left the extra ~1 cm not covered in glue, so I could hang it some where to dry.
Then I just cut the top of the banner, just like you've done, so I could fold it around a standard.
When the glue has dried, its good to paint on.
I guess, if you want some kind of wind in the banner, you can try to form it a bit, in the drying process.
I have a pic of the banner to support it, if you'd like to see it some day.
Hope it made sense
