I think the "sharp" taste is more than likely carbonic acid bite.
When you quick carb something, there is a strong "bite" due to the carbonic acid. That gets better pretty quickly, but it's one reason I never shake or overcarb the keg.
The flavors will meld better with some time, and should smooth out nicely. I think the reason for the low body ("watery feel") is the low ABV. A 1.044 stout isn't going to be full bodied and "chewy", especially if mashed at a cooler mash temp.
If it's at 40ish degrees, I'd probably turn it down a bit to 9-10 psi and purge the keg. That should help make it feel fuller and also reduce some of the carbonic acid bite.