Couple of problems with Edit Poly modifier (I think)

Hi all, my first post here! 🙂
So I've been following along with this tutorial, and all has been going reasonably well, but I've run into a couple of issues relating to the Edit Poly modifier. I'm using the modifier on shapes I've made from selecting the inside edges of the "pavement"/"sidewalk"s, and clicking "Create Shape From Selection".
Circled in red in my image, is an area that has vertices, but using Edit Poly hasn't given me a polygon there, when I think it should have! My second issue, circled in blue (in both perspectives) is that all of the polygons I created with Edit Poly are apprearing just fine in the perspective view, but in any view (like the top view) with High-Quality (shading? Not sure what the right word is) selected, they're really black and really flickery. Is there something wrong going on there too?
Any help would be appreciated, and I can upload the file if that would help.