Big, a 1/2 degree out is nothing and like Cyber says, easy to correct with the covering, even if it's an older plane like mine you can still get that out but I'm sure no one flying the plane would ever notice it one way or another.
Brian is building his Extra to compete with so going for perfect is always the best way to go.
I don't have any photos on file of one of my Extra builds so I'm not 100% sure but it seems to me I made up a full length jig for the wing halves.
For sheeting the wing I use thin CA on the first side then either medium or thick on the other. I do have a CA problem but for sheeting I want it to set right away so I use it. This time of year I can have my shop window and door opened so it's not a real big deal but during the heat of summer or the cold of winter it gets me. The CA adds no moisture so that may have something to do with most of my builds not getting much in the way of warps. That was a MUCH tossed in there, let he who is wothout warps cast the first bottle of glue. Brian, how big of warp did you get??
Gene