This is a guy who woke up with an itch and decided to act on it. "Me pegó la gana" [I just felt like it] is the whole philosophy of the song: he felt like having a drink, getting drunk and hiring a brass band, so he did, and now he is outside his crush's house with a serenade at full volume.
He is not leaving, either. "No me iré sin verte, vale más que salgas" [I won't go without seeing you, you'd better come out]. The noise has already woken the neighbours, tomorrow is Sunday, and he dares her to send out her parents or even call the authorities: "Que salgan tus padres, no hay cambio de planes" [let your parents come out, there's no change of plans]. It is cheeky and a little much, which is exactly the fun of it.
A few things a translation hides. He swaps the classic mariachi for a banda, the brass-heavy band of northern Mexican music, and asks them to play "El Muchacho Alegre", an old corrido favourite, yet again. Instead of roses, he has loaded his troca (Mexican slang for a pickup truck, from "truck") with cold beer. And "darte lata" literally means "to give you tin", but it is everyday Mexican Spanish for pestering someone, which is the most honest description of this whole night.