I traveled into the world of pen and thumb measurement next it got messy.
However, I realised something interesting as I painted over my attempt to see what was wrong with it. If I grabbed it with the pen tool and squished it ever so slightly to the left then everything almost aligned perfectly.
I realised that the second orange line I used for a grid line (right of my sketch's head) was too long. Mostly because I used my fingers to measure instead of the pen. That being the only line that made the difference is encouraging as it means the rest of my work was completely right.
I'll certainly practice this a couple more times before i move on to gesture drawings but so far so pleased. Much love.