Ours is a canvas awning - did that same thing in a windstorm and hubby stood on a ladder and resewed the seam by hand with marine outdoor rv protection thread.  I held the edges together while he sewed.  Was difficult in the wind, but we knew if we didn't take care of it , it would be damaged further.  We figured out that ours was stressed in that spot from the anti-flapper things you fasten at the edge.  We don't use them anymore,we just drop the front edge of the awning, or put it in if it's going to be windy.