My First Tournament Game!
Very good for a first tournament !
4...Bg4 (?) : I feel this is wrong, but it is not so easy to prove (as in the regular Philidor where after 3.d4 Bg4 ? there is almost a forced win).
5.h3 (?) looks like a mistake : 5...Bxf3 6.Qxf3 (6.fxf3 Nxd4) 6...Nf6 (6...Nxd4 ?? 7.Qxf7#) and Black has equalized (he will soon trade the c6 knight against the Bc4). I would play 5.c3, but of course that's not very active.
5...Bh5 ? is a serious mistake
6.Bb5 : again, I would play c3.
11.Qg3 !! deserves two exclams, as it is not easy, when you are offered a comfortable endgame (weak doubled c pawns + center pawns in favor of your bishop), to refuse the queen trade.
13.Nd2 (?) : I do not agree with your plan. The knight won't do much on f5. I would play the weird looking 13.Bd2 !? : it does not really lose a tempo because it attacks g7, and the idea is Bc3/Nd2/Nf3 pressuring e5.
13.f6 has the merit to trade bishops. Actually, this might be a good move in such a hard position for Black.
15.fxe3 ? : For the first time, I completely disagree with you. Better Qxf3, followed by Nb3 (blocking temporarily the b file and aiming the hole at c5) and Rd1, doubling on the d file, etc.
15...0-0-0 ? : Of course, you have to die of something, but obviously ...Ne7 could have put a real tough defense around the queenside weaknesses. Now White will just butcher the black king.
17.Qg4+ (?) : I don't like it, because you force the king to defend his pawns. 17.Qe1 already is a threat : if Black does nothing, 18.Qa5 wins the a pawn due to 18...Kb7 19.Nc5+ with a mate.
20.Na5+ does win the exchange at least. The critical line is 20...Kb6 21.Nc6 Rxd1 ? 22.Nxe7.
21...Rd6 (?) : there might still be a bit of hope with 21...Rxd1 21.Rxd1 Rd8 22.a5+ Ka7 23.Nxc5 Rd6, but of course Black should lose with one less pawn and an inferior position.
What follow are just details about how to win faster a won position, but not really mistakes.
24.Qa7 (?) : you missed the quicker 24.Nc4 Re6 (forced because of 24...Rd7 ?? 25.Nb6+ and Nxd7) 25.Qe5 where Black's pieces are completely tied up and the not-so-subtle Qa8+ threat is already hard to counter.
25.Nb7, as you mentioned, was also faster than the text.
26.Nc4 ! : my first thought was the elegant-looking Nc6 ?, but it does not lead anywhere.
37...resigns : I guess you have seen that if 37...Ra1 38.Ra5 ! and the pawn promotes, but I point it out for the others.
Spite checks...pretty blondes...chuckling to yourself at your opponent's moves...you're pretty lippy for a fella playing his first game!
Anyway...well done