Good stuff Andy. If the part has stuck to the mould, ease it gently from side to side, and back to front, which should free it without much problem.
The only times I've ever moulded resin parts, all I had to make the moulds was 'Plasticine', and of course the parts stuck to this. But by moving the part(s) as described, they broke free easily, and with minimum distortion to the soft mould.