Building my first tsugar /help with sao

Hello everyone , thank you for taking the time to read this and possible helping me.
I have a copy of Shamisen of Japan and am starting to build my first tsugaru shamisen.
The trouble i have is with de sou, i am a little troubled by the templates in the book as wel as the given sizes.
If i follow the size given for the width of the sao it schould be about 6.8 cm and looking at the templates of the curve and that of the tenjin this is to wide.
But folowing the templates the width of the sao woult turn out to be just 3 cm wide witch dousn’t seem rigth when looking at pictures etc.
Can someone tel me the correct sises for the sao ?

hi martin… do you speak spanish? anyways… I want to try and help but I’m having a hard time understanding your confusion when describing the parts and their measurements. If you speak spanish, can you try explaining in spanish? If not, can you make a simple drawing with the dimensions as you understand them on the book?

Hi Pablo.
Thank you for your reply.
I’m sorry to say but no abla espanol.
But no worries i figured it out thanks to the wold wide web.
So i’m building away on my firts shamisen.