I think jim asked a very fair question, which is a long way short of an answer.
Jim's pudding analogy is of an expanding euclidian 3D object, not a map from a 2D one to a 3D one.
This issue of the edge galaxies can be addressed in two ways?
How do we know (what evidence is there) that the inhabitants don't see an asymmetric universe?
The second is the current explanation which is by no means proven.
The thinking runs as follows.
Instead of the raisins being distributed throughout your pudding, imagine they are just popped onto the outer surface, as if they were spots painted on a balloon. So the zone of raisins or spots really is a 2D surface in a 3D world. In this model or analogy no raisin sees an asymmetric view as there is no boundary in the 2D of the durface.
Now let the dough rise so the pudding expand. The outer surface gets bigger and all the raisins move farther away from each other. There is stil no boundary so the raisins maintain their viewpoint.
Translating this model to our 3D universe, The most widely accepted explanation of theory and observable facts in modern physics is that our 3D space is 'curved' in 4D, just as the 2D surface of the pudding is curved in 3D.