As soon as you kill the Goddess, you'll get some dialogue and then it'll make a check for Anal Virgin, if you succeed in it (which you should have), you get the achievement, if you fail, you don't get it. So, if you have a save/quicksave from before you fought her, just do it again; and see what it says.
I mean, even if for some reason you failed, it really is so mind-numbingly easy to get, even on Ironman difficulty, you can actually just make a bee-line for it, get the achievement, and then continue your playthrough normally.