Hi. i don't know about your particular annexe, but we have a low sleeping annexe. It zips into the side panel of the full awning, you then pull the floor out square and flat , peg the corners down. Then you crawl inside and and take a pole that opens into an "n" shape and push it into the seam where the back wall of the annexe meets the annexe roof, adjusting the size to make it taut. Gyu ropes and pegs, job done. We don't use the main awning poles at all. Perhaps yours is different? Is it the sort that just hangs inside the main awning not like mine that protrudes to the side?
mel