I thought the same thing. The 37 ring is pretty thin in contrast to the groove that it fills and looks like it'll barely seal. Mine's been holding strong for almost a month now although I still kinda worry about it since that's where my original leak was.
I put my faith in hoping the ring would expand and create a better seal and maybe that's what mine's done because it's holding up.
But if I did have to do it again I'd go with a slightly bigger ring as you're suggesting just to be extra safe.