My Ascendant is Scorpio. And Sagittarius is in the first house. But Sagittarius is not completely in the first house, only up to 0° 2 minutes. And I have the Moon in my first house. So I have three chart rulers?
If the sign of Sagittarius is intercepted in the first house, meaning it is entirely contained within it, then Jupiter is also one of your rulers, along with Pluto, Mars, and the Moon. Otherwise, it is not.