You can do it as a two piece, though sufficiently tensioning the skin - depending on the weight on the nylon you have - might be a problem.

But, sewing a seam is uncomplicated and, more importantly, it is very easy (but annoying) to undo the section you've just messed up and re-sew it. Use a batten or center ridge to help keep the seam straight.

From what I've seen, a straight seam is pretty darn rare, and ultimately irrelevant, in any case.

I assume the video you refer to were the skinboat school's vids? If not, do check them out!

If you can build the frame, you can sew the skin - have faith!

Dave