Alternatively, find a long (8' is nice) batten - I used a length of 1/4" X 3/4" fir molding - and lay it on your 'points.' Curve and bend it to conform to the shape described by the points, making certain to include *at least 4 points* at all times, the more points you include the more true your scribed lines will be. You will find you don't have enough hands for this - no problem - use some weights, anything will do. I used small paint cans, glue bottles, rolls of duct tape, to hold my batten to the points, then gently scribed my lines with a #2 pencil.
There are probably other ways to do it too, but the above (not the beetle!) worked for me!