Seriously, if you are going to make your own sails, even if you make them from one panel, make the luff (Where the main joins the mast) sorry to explain like this, but don't know your knowledge of sailing. Any way the luff needs to be curved, so that about 2/3rds up the sail is max curve, and this measurement needs to be upto 10mm, no more, this will put curve in the sail panel, and also when you tighten down on the kicking strap you won't get a crease from the tack to the mast. giving the panels shape also helps, but I can't explain here how to do it.
Andy