Disclaimer: having not played SM, I don't actually know what this wormhole looks like, and I might be missing some crucial information that renders all this information unviable, but here's what I got:
It is possible for a three-dimensional object to be seen as two-dimensional. Our perception of depth comes largely from our ability to see shade. Notice how the circle looks like a sphere because of the shading:
However, if an object were to reflect no light whatsoever, it would look perfectly two dimensional. And yes, there is a material like this. Ladies and gentlemen, I give you Vantablack, the darkest material known to man:
https://www.youtube.com/watch?v=9v0_fID_jvA (okay, that's not technically Vantablack, but it uses an extremely similar technique and has the same effect, and this video demonstrates the idea very well).
Unlike, well, everything, Vantablack reflects almost no light at all, so, even when applied to a three-dimensional object, you can't notice any details popping out, and it looks more like a 2-dimensional silhouette.
Once again, if I'm missing something and this isn't really applicable to the situation, I'm sorry, but at the very least we learned something fun today, right?