Depends on the breed but yes the first eggs are smaller and they get bigger but if you have a breed that lays smaller eggs they may never be bigger than the store bought eggs unless you have the same kind of chicken like a leghorn or a white rock.
The first eggs a bird lays are called "pullet eggs" and are always teeny tiny. Give them a month or two, and they'll stop laying practice eggs and start laying their true size egg. Egg size can also change with the season and the weather.
Whether or not these ladies can ever start laying a size Large is going to depend on whether or not you have an Ameraucana or you actually have an Easter Egger.
If you bought your Ameraucana from a breeder, then it's entirely possible that this is as big as it gets. Call the breeder and ask what size eggs his/her birds lay. My true Ameraucanas lay a medium egg.
If you bought your bird from a feed store or hatchery (other than Meyer or MPC) then you have an Easter Egger. Easter Eggers, being mutt chickens, can lay any size of egg, but IME they are bred to lay more and bigger eggs than true Ameraucanas. If you have an EE, then I would assume that the egg will end up being at least a "large" on the scale. My EEs, some from Meyer and some from Murray McMurray, lay anywhere from size large to size jumbo eggs.
(based on the green color of your egg, btw, I assume that you do have an Easter Egger, not an Ameraucana.)