I was thinking of something similar, sun screen from the awning down to the ground. Perhaps your idea , a solid windscreen would be more useful.
I would attach some aluminum channel to the end of the awning similar to the type used for lighting
strings, if there is not something there like that already.
If you cut the tarp with hollow curves on the edges, two stakes would hold it and keep it from flapping.
A hollow cut means it is not cut in a straight line but has less material in the middle and more in the corners. So the middle is always under tension.