Strange...the turtledeck instructions on my GP kit had me starting from the bottom.

I got the best results (on the very last piece of turtledeck sheeting that I had to do by the way) cutting the sheeting to size as per the instructions, wet it on one side with ammonia/water. curve it around a glass bottle (in my case a nice 1999 Shiraz that had to be emptied beforehand) hold in place with masking tape until COMPLETLEY DRY. The curve of the bottle does not need to be exactly the same as the finished curve of your turtledeck, you just want to get it in the ball park.

Once the sheeting is dry, fit it to the part of the airframe where you want to start gueing and trial fit. Once you are happy, tape it down along the long edges and let it cure!.

I glued mine with wood glue, gives you some time to mess around.