Had a section marked in chalk where it was still pulled in a bit. Hammering from the inside out against this steel block got all but a section above the weld area flush.
Used the shrinking disc on the inside along with compressed air to cool it to push the low spot outwards. Nice and flat right across now.
As I was tacking the other side, this end lifted even after planishing the tacks as I went along. So stopped to rectify it. Fully tig welded the section tacked and then planished only the area around the side to raise that part which brought this end down back to perfect.
Finished the other side off so getting there. Have to make the pieces in between now. The curves outside the window frame are different to the ones on the inside. Two pieces make up the bottom and four pieces for the top.