Hello,
Since he is still so young, I wouldn't worry about it. Its probably just taking its time growing in. The next time you take him to the vet you can ask about it, but I don't think it is much to worry over. I think it will probably grow in soon. Maybe every couple days take pictures to see if its getting better or if its getting worse. (Its always hard to tell things like that by memory if it is slow changing).
He is adorable, by the way!!!
