Robert.
I had a Ultima 260 and had pretty much the same problem. Although on some occasions I got it to fit perfect. I think it's something to do with ground levels. I did manage to get the bottom touching the van but used to have big gaps halway up which i could stick my arm through.
If I was you I would go for a refund and have a look around. You can get the same sort of awning which has poles at the back to fit snugly to caravan. I saw on on display at Highbridge Caravans, their website could be worth a look.
Good look, Dan.