Cut along the cut line and fold the hem at the sail outline. You want the hem on the starboard (right) side of the sail. I like to lay a length of 1/8" line inside the fold to reinforce the edge a bit.

I sew the hem down, others use double-sided sticky tape (like carpet tape) and still others use both.

For sewing, I use a standard sewing machine with a #16 needle and upholstery thread or Dual Duty XP Heavy by Coats and Clark. I tighten the resistance on the thread quite a bit (8 on my machine) to keep it from bunching up on the back side. First, I put on a welting foot and run a straight stitch as close as possible to the reinforcing line. The next thing I do is go around the edge of the hem with my machine's widest zig-zag stitch.