Good King's Gambit Study for the Endgames

When I reached the Endgame, I wanted to have the black king as far away from my passed pawns as possible.

Then once I got a queen, I swapped my queen his pawns to stop them from promoting, Then I kept my final pawn to win the game using the "Box" technique.

Here is the game.

If you guys have any feedback on what I could've done differently, please feel free to do so!

When I play an aggressive opening, I wish to mate my opponent by move 20. If I wanted an endgame, I'd play a queen pawn opening.

Understandable but I wanted to play a gambit opening. Plus, I have been playing this opening for some time now, and having some great success with it.

Good job. I’d say you could work on your Queen and King Mating patterns. Took you a while to mate him.

Q+K vs K takes ten moves at most. 20 moves is way too long. The box technique is about restricting the opponent's king squares with every move, it was not implemented correctly : correct is 67. Qd5 followed by Kg7 and Kf6, which is mate in 4.
White would have not won this endgame without the horrible move 43... Kb7 (I am discounting the double miss at move 39-40 because it involved some calculation in the battle for tempo). All in all this pawn endgame is not really favourable to White, so it was sensible to play 36. c4 and make a comfortable draw (and maybe more if Black keeps making moves like Kb7).

54 Qxb2+ is unnecessary, this pawn is easily winnable. The next pawn is won even easier. So you gave up a queen twice without a major reason. Well, your method works too of course, but as a study no, it's not a good one at all, sorry. What would you have done if b2 pawn had been the only one on the board on move 53 with just your queen against it?

UPD Well ok, technically the first queen sac leads to a faster mate (several moves less) than if you just go for the b2 pawn, but after that your second pawn promotes and there's no need to invent anything, just mate him straight away. Still, it would be a more interesting exercise, like "win the b2 pawn without moving your other pawns".

I was going over my game after I played it, I saw the faster mate with the help of your comments, now this makes more sense for a faster mate than the way I played it. Thanks, guys!

@Checker99 Going over your games is a great way to improve quickly. In that regard, do you know about the tablebase feature? It is opened with the same button used to get the opening book; that button that looks like a book at the bottom left under the score of the game.

After Black's 66...Kf6, look in the tablebase to see faster mates.

Of course the issue with that is that humans needing a procedure for these mates. Patterns to remember. The box technique you mention is one for this ending of KQk. Another is to put the Queen a Knight's move from the opponent's King, and then mimicking his movements until you have him trapped on an edge (but NOT stalemated). Then bring up your King for a King and Queen helper mate. See my study here for a full explanation: