I didn't take a camera on this past trip, but here is a quick diagram of where I put the strap. I removed the two straps at the rear that came with the bimini, and attached one of them to the middle of the rear cross bar.
I did this on the river, so used duct tape to protect the fabric from fraying. If I'd done it at home I would have removed the bar and used a sewing machine instead of the duct tape.
I also reversed the bimini and put the "front" at the rear of the boat so that the frame would lie flat on my deck. (As designed by the factory, the rear frame/bow has a curve near the lower hinge point that would not allow it to lie flat.)