That's strange about the smell of the tape. I wonder who is supplying Sailrite? I've just bought some tape that looks exactly like https://www.sailrite.com/Seamstick-3-8-for-Canvas-60-Yds with no branding visible. My throat is very sensitive too, and aromatics will have me spluttering, but I can put this tape literally against my nose and can't smell anything. Neither could I with the tape I bought previously, which was branded 3M.
I agree with Arne about the effect of scale. You are trying to do full size seams and hems on a small piece of cloth, and it's bound to be difficult.
I suggest you make a test piece which is exactly to Arne's method B seam and batten pocket, but with straight edges. It need only be a foot or so long. Lay two pieces of cloth a foot square one on top of the other, and sew with straight stitch 3/4in from the edge (no more) to join them. Cut a piece of cloth a foot long, and wide enough to make a pocket 20% bigger than your batten diameter - I'm guessing 7in. Stitch this on according to method B, either straight or zigzag stitch. If you can do this, you can make a sail according to Arne's methods. The hems (tablings in sailmaker's parlance) are straight, so whether you do them the way I do them in canvas, turned in twice, or Arne's way, turned in once with webbing on top, they shouldn't present any difficulty.
Don't worry about curved edges, they get easier at full size.