I already played this tournament in a real life team championship.

Looking over the game, I see an illegal move by my opponet. Do we have to play again?

He castled through check of my knight. For some reason, I calculated that part out looking at forking his king and rook since he can't castle then after the variation was played, I forgot and took his rook with my knight.

Do I have to replay the game? Will we get in trouble?

You're in luck. You and your opponent can play stacking the pieces for an hour, declare a checkmate, and the result would stand. At least if the TD never noticed.

It may sound funny but under USCF rules illegal setup and moves stand once the game has ended.

and if we noticed 5 moves later?

My previous question also stands.

If you don't see it when it is played, then you have missed your chance to say anything, once I was playing a chap, he moved h3-h5, after a minute of letting him think this though I politely informed him of his illegal move, you can't reply the game, the game has ended, like football, (you don't reply the game because the ref missed something) watch out, some players will ALWAYS try to play illegal moves, 

i think your game is very nice  after 11 ...Nb*d5 here i think your position in white is better look you play scadinavien 1e4 d5 2e*d5 Q*d5 3Nc3 Qd6 4Nf6 d4 5g3 a6 6Bf4 Qd7 7Bg2 Nc6 8Nf3 g6 9Qd2 Bg7 10 d4 Nb4 11a3 Nb*d4!! here i think blak play a wrong move

You could always claim that you win faster if he doesn't castle: if you won anyway it would be a bit like discounting a goal because the defenders conceded a penalty.