Welcome to the Bunnings Workshop community @Gordon2. It's great to have you join us, and many thanks for your question about Bistro Blinds.
Would there be enough room to fix a Bistro Blinds 0.75mm PVC Outdoor Blind - Clear / Black 2400mm x 2400mm on the outside face of the opening? You might find that the zippers align perfectly just inside the posts. If you still had the packaging and the blind was in a saleable condition, you could return and exchange it. Alternatively, I'd recommend you chat with one of our helpful Special Order team members at your nearest store. Bistro blinds alter some of their blinds and accessories, so they might be able to come up with a solution.
Please let me know if you need assistance contacting your local store.