You've never held a perfectly smooth sphere. The earth is a much smoother surface than a billiard ball. There's no edge conceptually, in the same way that vacuum is not missing air, it's nothing. It warps spacetime in a way that you can't discern an edge. Likewise there is no "inside" a wormhole. It's a hole in three dimensional space that leads to another point in three dimensional space. There's no "inside" because that implies a point that exists outside our universe which based off our current understanding of physics, is impossible

We literally don't have the language to describe these phenomenons because humans are three dimensional creatures. We can't imagine these concepts because it involves a reality we can't perceive. It's like asking someone to imagine a color they've never seen. We can't do it