Peda is a very common slang word in Mexico for a party, specifically one with a lot of drinking. It can also refer to the state of being very drunk.
In the song, Becky G tortures herself by imagining her ex "en la peda" (at the party), with another girl. Using this colloquial term instead of the more standard word 'fiesta' makes the lyrics feel more raw and authentic, giving you a taste of real, modern Spanish.
We have all been there: sitting alone in a dark bedroom while all our friends are out partying, staring at unposted photos and looping an old shared playlist. That is exactly where Becky G starts in "2NDO CHANCE". Instead of moving on, she admits she is torn between love and hate, spiraling over the thought of her ex out at la peda (the drinking party) doing with someone else what they used to do together. In Mexican slang, peda comes from pedo (drunk), meaning a lively night out drinking with friends. The desperation gets so real that she asks for false comfort, begging him to say he still loves her "aunque sea mentira" [even if it's a lie].
Ivan Cornejo jumps in to give the other side of the breakup, and he is just as wrecked. He throws a little shade by recalling her dramatic past promises, noting "Recuerdo que decías / Sin mí te morirías / Pero sigues viva" [I remember you said / Without me you would die / But you're still alive]. He admits his pride took a beating after believing he was her exact type, leaving his world completely dark without her. Both singers get stuck in that messy, relatable post-breakup phase where you would rather hear a comforting lie about getting a second chance than face the reality that it is actually over.