Looks like the hammock needs to be between 13' to 15' in length to accommodate the length of the stand. Your hammock will be shorter than the frame. Either the hammock or the stand should have come with two short lengths about 8 inches long so you can adjust the length to kit you needs.
12 should work fine. I have several chains of different lengths with steel "S" hooks for connection from hammock to stand and I was about to say they came with the stand but I think they might have come with my hammock.