At this point you will need a second person to help you position the entire attic ladder mechanism through the opening into the attic space. With one person in the attic and one person under the opening, insert the attic ladder into place, ensuring that the door is flush with the ceiling.
Drill two batons across the bottom of the opening; the attic door and frame will rest on these batons as the frame is attached to the surround. The person in the attic can now screw the supporting frame to the attic ladder frame. After the attic door is secured into place the second person can unscrew the batons from below and open the attic door.