"Thinness" of body typically doesn't change much from green to mature brews in my experience. You're probably stuck with it. If anything, thicker/sweeter brews dry out more over time, not the opposite. Maybe you added too much water at the end? I've made that mistake before.
But, really, it's been my experience that the hoppiness in alot of IPA's needs a bit of sweet malt backbone to balance it out. In that light, FG @ 1.012 sounds a bit low. My IIPA that is dryhopping right now finished out around 1.030, and it's delicious right where it is. Oftentimes, dryness (low FG) can be perceived as thin body, and this might be the case here.
Unfortunately, you've already bottled. Otherwise, I would have suggested just what I did last time I had a beer end up too dry and watery: a supplementary boil with steeped grains, hops and maltodextrin. Add that to the secondary and let it meld with the rest of it.
Next time, judge the body/weight/mouthfeel of the beer as best you can before you bottle it, and if you need to amend it, you can. Maltodextrin is a brewer's best friend in this case.