Hello,
This is my output for k=12:
12
0 2
1 2
2 1
3 0
2 -1
1 -2
0 -3
-1 -2
-2 -1
-3 0
-2 1
-1 2

But I don't understand why I get "Wrong Answer" for the k=12 test.  Is it really possible to solve 12 with less than 12 fences?

No, for k == 12 U require exactly 12 fences. My AC program gets output very similar to yours. Perhaps, WA is at another test.

Yes, I submitted the same program again today and I got accepted!  Maybe they took out one of the tests?  Or perhaps I had been submitting to the wrong problem!