Congrats, you discovered Legall's mate. It's an old one that has been talked about a lot. In fact, it was on the front page last week.
It's not exactly a gambit seeing as it results in mate. A gambit is when you give a pawn or piece with positonal composition or something as the reason. This is much more of a sacrifice style thing than gambit.
This is something I'm sure plenty of you have seen before, and I'm sure there's a name for it by now.
This game begins with a very standard opening; white is aggressive, black is more passive-aggressive. With black's king's knight undeveloped, this mate comes pretty easily as most people can't help but take the bait.
I came across this gambit a little while ago and occasionally the opportunity comes up to take the shot; one player actually took the knight instead of the queen and then said "oh no I can't believe I missed your queen" haha, so it didnt work out but I was able to recover quite well, anyway.