Maghrib End Time?

Assalamualaikum warahamatali wa barakatuh

So I started praying magribh after the sunset but by the time I finished it got dark and the rays of the sun vanished.

I'm confused as to when the time ends as some say it ends after all the rays of light has gone but then some say at the beginning of isha time when it's completely dark and the white twilight has disappeared . Also do I have to redo the prayer?