Adueñaste comes from the verb adueñarse, meaning "to take possession of" or "to make something your own." It is a stronger, more dramatic word than simply "to take," suggesting total, almost territorial control.
In the line "Te adueñaste de mi vida inmediatamente" ("You took over my life immediately"), the singer describes falling for someone so fast that they instantly claimed every part of his life and feelings.
Have you ever met someone so small who takes up the biggest space in your heart? That's exactly what Camilo sings about in "Chiquita"! He's completely smitten, describing how a tiny person's "pisada de hormiguita" [ant's footprint] leaves an "huella de elefante" [elephant's footprint] on his heart. It's such a sweet and funny way to say how much impact this person has on him.
He talks about how this person immediately took over his life, and he's even a little scared of losing them. Camilo wants to slow down time because he loves spending it with them. He's ready to hold their hand, even if sometimes it feels like they only want to hold onto just one finger. And when he has to leave, it hurts more and more each time. He just wants them to say, "Tú pídeme que me quede y me quedo" [You ask me to stay and I'll stay]. It's a beautiful song about deep love and devotion, and you can really feel how much he adores this "chiquita".