Thermostat Questions

I know this is a stupid question, but how big is the hole in the thermostat gasket supposed to be?

I bought a felpro 35063 gasket and placed it over my thermostat and it barely overlaps the edge. I'm thinking either the thermostat is too small, or the gasket hole is too large.

btw- when I place the thermostat in the upside-down housing, there is a gap between the edge of the t-stat and the outside of the recess in the housing. Isn't it supposed to be tight??

How much gasket overlap should there be between the gasket and the t-stat?

Thanks guys. It's been years since I've swapped out t-stats and my memory is fading. The FSM wasn't too helpful this time either.