You mean North Carolina? Actually I think the last few polls released before the vote had the Marriage Amendment winning comfortably by double-digits. Even so, it is true that the Amendment’s ultimate 21 point victory was higher than any poll had it winning by.
The only poll I can remember showing majority opposition to the Amendment was some poll done by, I think, Elon. It was so wrong, and such an outlier, that its hard to believe that it wasn’t fixed.