Finishing: I managed to block it exactly to size however when it still was not dry after three days of cold and damp autumn weather I air-dried it flat in my dryer (why had I not thought of this before?) and this worked very well. Adding a dryer sheet gave it a nice fresh scent, too. In the end my son had started a fire in the wood stove and the heat did the trick and dries the jacket nicely. It feels nice and soft now, too.

Second attempt: After doing the math calculations I converted the pattern to suit my yarn which gave me a gauge of 19 sts and 20 rows= 10x10 cm. The pattern is based on a gauge of 24 sts and 48 rows= 10x10 cm.
I am knitting the two front pieces up at the same time taking yarn from the center of my skein and from the outside of the skein this way I don’t need to think about what I did when working on the second piece and I will have both on my needle when I start on the back.
It is already looking much better than my first attempt.

First attempt: Since this yarn is thicker than the one called for in the pattern I used the instructions for the smallest size hoping that I would achieve the next size up which when measuring it did. However my mistake was that I thought the next size up would be 3-6 months when in reality it is 6-9 months and I thought looked way too big to give as a gift for a newborn.