Be glad it at least sort of covers the door. When we were looking at trailers there was one I saw that had dual entry doors. And the awning smack dab in the middle of them, covering neither.
Based on your photos, I'd say you have two options to keep the door dry:
1) More expensive option: Move the entire awning over so the arm is on the other side of the slide out. Depending on how big your slide is you might need a bigger awning to boot.
2) Redneck option: Drape a tarp on that one side of the awning. To avoid water coming in you'd need to ensure the tarp goes on top of the awning, then run ropes across the awning to the front. Make sure you slope the front down to let water runoff in that direction. Next, at the bottom of the tarp you'd want to run those to some kind of tie-down so it's not flapping around on you.
Note: If I were to attempt option #2 my DW would divorce me. She hates when I 'concoct' stuff like this. But it would block the rain.