Boceto translates to "sketch" or "draft". It's a less common word in everyday Spanish songs, making it stand out.
In the lyrics, Tiago PZK uses it metaphorically to describe a relationship that had potential to be a beautiful "pintura" (painting) but ended up as just a "boceto en la basura" (sketch in the trash). This imagery powerfully conveys the idea of something unfinished and discarded, adding a layer of artistic melancholy to the heartbreak.
In "Me Olvidé," Tiago PZK sings about the painful end of a relationship and his efforts to move on. He feels like he was a victim of a cruel game played by Cupid, where he loved blindly and gave his heart away, only to be betrayed. He uses powerful metaphors to describe their failed romance, comparing it to a masterpiece painting that ended up as a "boceto en la basura" (a sketch in the trash) and a dream of going to the moon that they weren't good enough to achieve.
Now, his focus is on forgetting the pain. He declares, "Pero de eso me olvidé" (But I forgot about that). His way of coping involves going out, drinking, and talking to new people. He claims to have thrown his heart away because he's afraid of getting hurt again. He tells his ex that she was like "un infierno" (hell) for him and that he has deleted all their old photos, making it clear there's no chance of getting back together.