With the middle in position, just move to either the front or the back and repeat; only this time you will also pull a little towards the front and the back. Remember, you are only gluing one-third of the way at a time. If you've got a couple of helpers, they can hold the front and rear corners up and away from the roof while you are pulling at the center. Once you have the top pulled into place, press it down firmly with your open hand. Then, fold the top back again and brush more cement over the next third of the way and repeat the process until you get to the edge.