How to Castle in Chess960

I am playing white in a chess960 game and my king and left rook are clear..no threats on castling squares and no king moves till now..Can't seem to castle in Chess960 games and white always seems to get advantage post castling in Chess960 games that i play 

The game PGN starts from the line below :

[Event "960! Revenge? Easter Island vs The King Attackers - Board 12"]
[Site "Chess.com"]
[Date "2016.09.04"]
[White "guruprasad88"]
[Black "JOSEDAVIDAGUILERA"]
[Result "*"]
[WhiteElo "1816"]
[BlackElo "1516"]
[TimeControl "1 in 14 days"]
[Variant "Chess 960"]
[SetUp "1"]
[FEN "rbkrbnqn/pppppppp/8/8/8/8/PPPPPPPP/RBKRBNQN w KQkq - 0 1"]

1.d4 c6 2.c3 Bf4+ 3.e3 Bh6 4.Bd3 f6 5.Nhg3 Nfg6 6.Bd2 Bf7 7.h3 d5 8.Nh2 e5 9.Ng4 Bg5 10.Qf1 Ne7
 11.dxe5 Nhg6 12.exf6 gxf6 13.f4 Bh4 14.Ne2 h5 15.Nh6 Qg7 16.Nxf7 Qxf7 17.g3 Bxg3 18.Nxg3 Rg8 19.Nxh5 O-O-O *