Hey really sorry this didn't unlock properly for you.
If you've gotten the golden rod, you should have gotten the achievement.
When you check the fishing journal in your inventory, are any of the fish still blacked out?
Also, you've turned in every single fish in your current inventory?
Also, if your Xbox was disconnected from the internet when you unlocked the achievement, it may not appear until the next time you boot up the game connected to the net?
And yes, unfortunately, if the file is truly bugged, then you may need to overwrite your save, which would suck.
The issue may be able to sorted out with a patch, but it would be a while before that goes live.