First and foremost, wormholes are theoretical, and there are a few different kinds of them. A Schwartzschild wormhole is technically non-traversable, and has many, many other problems being compatible with this questions, so we're going to ignore it and go with a Lorentzian wormhole. This kind is purely topological, and it would link two points in space in a topological manner. Of course, this makes you question not make a whole lot of sense. A Lorentzian wormhole is not like a bridge, but more like a hole in a sheet of paper (in three dimensions it's a sphere, but that tends to much with our limited brains, so nearly all wormhole analogies are 2D).
Imagine that you have a sheet of paper that you twist into a mobius loop (because this makes the whole thing easier). You now have a continuous flat region, which we'll call space. If you cut a hole in the loop, you now have linked two points of that flat space together--you travel into the hold, and you are instantly at the other place. If you make the hole bigger, you're simply making the point at which you traverse to the other space bigger. There is no "intermediary" part of the hole, there is only one region, or the other. You couldn't "expand the wormhole so that the whole station is suddenly inside the wormhole," because the "inside the wormhole" isn't a thing. You could argue that "inside the hole in the paper" is inside the wormhole, but that hole in the paper is the same as all the 3D space not on the paper-some sort of vague elsewhere that is not part of the universe in our analogy.
It would still collapse, but that's because anything traversing the wormhole would cause it to collapse, in theory. An Ellis wormhole (a vacuum solution to the Einstein field equations which is a Lorentzian-type wormhole) would require a negative energy density to keep it open (which isn't forbidden by our current model of physics, but certainly isn't predicted).
What would happen to the station if it tried to traverse an unstabilized wormhole? Well, it depends on the wormhole type. No matter what, the wormhole would collapse. Some Lorentzian and all Schwartzchild wormholes are also black holes, and now you just have a black hole. An Ellis wormhole theoretically isn't a gravitational well, and has no event horizon, so it may not become a black hole, but anything attempting to traverse it would definitely be in a bad state. It wouldn't make it through the wormhole (the collapse would happen before that), but after that I'm not entirely sure what would happen.
This answer has been long and rambling, to here's a quick summary:
- Most wormholes are also gravitational singularities. You can't get out of the singularity, even if you traverse. If it collapses, you get a black hole.
- There exists a special case that is not, known as an Ellis wormhole (a special case of the Ellis drainhole). If it collapsed, I'm not sure what would happen.
- There is no "inside" a wormhole, the same way there is no "inside" a portal in the game Portal. You're in one region of space or the other. You can enlarge the boundary condition, but then you simply traverse sooner, when you hit the "horizon" of the hole.
- Wormholes are mad theoretical, so all of this is technically nothing more than conjecture, backed by some interesting math.
