So as you've set things up, the radius of the sphere we can see is 13.8 billion light years. That means that the diameter of that sphere is 27.6 billion light years. But here's the rub, the visible parts are all moving away from us, so while we see them as being 13.8 billion light years away, they've been traveling for 13.8 billion years away from us. Along with that, the rate that they're traveling has been increasing the further away (in time and space) they are.

Now since we've found ways to correlate the distance and velocity that things are traveling on large scales in the universe, we can actually figure out about how far away the objects we can see should be from us, after traveling 13.8 billion years. This is where the 93 billion light year figure comes from, how far away those "edges" have traveled since they emitted the light we see today.