That's the correct rubber gasket, though yours is overdue for replacement. air cleaner may well not sit flat on that carburetor even once you've got a new gasket; it's not a match. It's a '61-'69 style air cleaner base on a '74-up carburetor that originally used a very different air cleaner. If this is what's going on, you may "get outta jail" with two stacked gaskets between air cleaner and carb.
And yes, the white cap needs to come off that float bowl vent in a hurry.