I've had finishes pool at the edges (it's called "fat edge") and then be gummy when sanded and not sand out like the rest.
I agree with the others that it looks like you've sanded through to the wood, but if you put more poly on the bare wood, it should begin to look like the rest of the finished area - if it's not, that's perplexing.
The witness lines that Epicfail mentioned are a concern, but if you sand without such a heavy hand from here on out, you just might get away with it.
I'd try using a small artist brush to put a few coats of poly on just the sanded through areas. If that evens it up, then I'd continue to add more coats to the whole thing. If it works out, you're golden; if not, you're back to stripping and starting over.