Hmmm, so, I'm assuming it's pulled over to one side, and clearly visible in relation to the barrel?
Did you buy it used, and maybe get one of the defective ones that were supposed to be destroyed? I still have my original rail that was replaced under warranty, with the caveat being that it was to be destroyed if I didn't send it back. I didn't destroy it, but, know better than to release it back into the wild, so that some other unsuspecting doesn't get screwed over.
If it's new, I'd get it replaced. All the NEA rails I've seen that are in spec have mounted up just fine, and are square. You either got a bad one legitimately, underhandedly, or there's just something funny about how it interfaces with your barrel nut. When you rotate the rail into place, was there a lot of resistance, or none at all, with a bit of wobble before you tightened it down?
My original reail simply twisted loosely into place, and was wobbly, requiring me to tighten it down. As I tightened it began to pull to one side.
When I got my replacement, the rail was quite snug being indexed into place, and tightening the screws didn't change it's alignment.
I also had the barrel nut on/off this rifle, and have no doubt that even the slightest barrel nut alignment would have an impact on how the rail connects, as, the barrel nut moves towards the receiver as it's tightened, ergo affecting the tolerances of the internal channel in the rail that is designed to square up to the teeth on the nut.
That's about as much informatoin as I can provide on the NEA rail/barrel nut interface. I'd say it's obvious you got a bad one. The quesion is, do you have an recourse with where you got it from, or is there a different underlying issue?
I remember how much I fought with my original rail before I found out it was a warranty issue and was able to get it replaced. I think I was one of the last ones to find out, but was told there were only about 12 or so that were like this. I'm not sure I believe there were only 12, and the question I have is, did you get this new or used?