So under the rules, it doesn't say anywhere that you HAVE to play as the 1 in the 1v3s, but I was under the impression that we had to. Can the rule regarding that be specified?

Personally, I think the 1v3 section should be played as the 1 so that you are the technical winner, but the only minigame where playing as the 3 benefits you is "Bob-Ombs Away," so I don't really care either way.