Excellent bow Steve, congrats mate. Very impressive.
If it helps at all, most warbow guys use no more than about 14 strands of FastFlight, right up into the 150# bows. I don't know if a shorter bow makes any difference, but I wouldn't imagine so.
I went through the exact same confusion on my latest 125# self yew warbow - the string just kept stretching over and over again despite it being FastFlight and despite the strand number being common. It ended up being down to my Flemish twist - I was so used to making strings for bows in the 70# region that I just wasn't adding enough tension while laying in the loops, and it was those that were coming undone constantly. I tried again really pulling hard at every step of making the string and keeping the wax to a minimum and that string held. It's actually a 12 strand FastFlight string, with simple Flemish laid in loops at each end and sits on a 125# warbow with no stretching or slipping at all. Might be something to consider?
