For anyone who may be interested, I have managed to fix the problem. I warmed up the engine shed with an old hair dryer. I needed to put a lot of heat into, but eventually the resin became malleable (I would say it had the consistency of semi dried clay). I then just supported in the wall in the position I wanted it and let it cool. It took a very long time to cool down, the resin held on to the heat surprisingly well, but it got there in the end.
I also took the opportunity when the windows were removed to repaint it. From the factory, a single colour was used to paint the whole shed (the green off the roof trim was also used to paint the bricks, it was done quite well, but wasn't to my linking). I added some variation and called it a day. Still going to add some detail around the window and door tops however.