Brian,
I don't know whether I can help you very much but I believe that if you cut dacron with scissors it will fray out. I believe that the model sailmakers use some kind of hot blade as it seals the cut. I was, once in the past, advised to use a soldering iron with a blade type tip but tried it without any success and, in the end, got them professionally made by Sailsetc. From what I remember they were not too expensive and were lovely sails cut to my measurements.
Derek.