I now plan on not just using csm but using a lighter woven fibreglass in 1 or 2 layers so i can safely remove part from mould then check there is no/little shrinkage by refitting the part back into the mould. Once i am happy, apply multiple layers of csm to build the thickness of the mould. 

I do remember your post though, and I'm sceptical that your demoulding issue was due to shrinkage. Your part is simply not designed to come out of a one piece mould, and the reason it is so tight to get in and out of the mould is because you have opposing angles in there that are too tight. You need to either change those angles to give yourself a bit of draft, or you need to make the tool in more than one piece.