I still feel confident it's A. stellatus, but I agree A. mappa is a possibility given its small size. In any case, it would be really helpful Kevin if you could post additional photos as it grows. There is a paucity of photos of juveniles of either species, and it is always better to document colour changes in a known individual, rather than string together photos of different individuals from publications or the web (some of which may be incorrectly identified).
Tony