I think I know why I made some of those mistakes:
It's pretty hard to see, but whilst wikipedia says that the first stage is 11.7m tall, the Users manual says that it's 11.2m. The second stage is the same in both cases, 8.39m, and so is the third stage, 4.12m. The AVUM upper stage is 1.7m on the wiki and 2.04m on the user manual, but this is because of a conical payload adaptor (?). I also messed up the fairing thanks to the fact that the value in the blueprint is equal to the value of the payload it can hold,
User manual I used:
https://www.arianespace.com/wp-content/uploads/2018/05/Vega-Users-Manual_Issue-04_April-2014.pdf
Wikipedia article:
Vega (rocket) - Wikipedia
not to the actual outer diameter.
Alright, I've had enough, I've screenshotted the Vega rocket from the official manual, printed it and cut it up into the stages so I could compare, (this isn't 100% precise, but it can tell me if i'm close enough).
And here's what I have:
The fairing being a bit slimmer is the most obvious thing, I've also made the AVUM upper stage a bit more accurate. I've also made the first stage 1/2 meter taller, and the interstage between the first and second stage is a bit closer to reality (I hope, I don't think that
aerodynamic skirt thingy was supposed to be there).
I hope this all made sense, but if it doesn't...
¯\_(ツ)_/¯