You needed to add more milk/cream/sugar and to let it cool slowly. Choc no like quick freezing. When melted shd look all shiny then pour. Sheen on surface. Need good quality choc too not just Cadburys. Don't get it too hot either when melting do on bowl over hot water. Slowly does it. Experiment on a bit of greaseproof paper first see how a thin layer sets. Shd be fairly instant when correct. Keep at it will work!