There is a way to check this out: Armed with the dimensions of the proposed sail, take a length of light line at least as long as the total of all three sides. Tie knots in the place where the three corners of the sail would be, ie tack, head
and clew making a pseudo-sail. Hoist it by the "head", attach the tack at the normal tack point by the chain plate
and tie a sheet onto the "clew". With it hoisted taught but not stretched try tightening the sheet. If you can get all three sides of the "sail" tight at the same time, the real sail can be properly trimmed.