No, i dont think you have done something wrong - however i read somewhere in cliffskis blog that you have to downloaded the extra maps once its patched. positech.co.uk/cliffsblog/?p=1076
Now I had already downloaded from that link and changed where the file was to install inside Steam and as I said it didn’t work.
But…I did it again (changed location correctly etc.), then went into my GSB folder in Steam and there was a rogue GSB folder with the campaign files inside.
A quick copy and paste and voila it all works as it should.
So thanks kemp as tbh I wouldn’t of retried again for a while.