Birman

Has anyone had a problem with a huge gap between the root ribs when trying to join the wings? I have a huge gap in my wings. When I lay the edge of a straight edge along the root ribs, there doesn't appear to be any gaps. However, when I try to join, the gap is there. I am afraid to start sanding because I don't really know where to sand due to the straightness of the root ribs.

Has anyone else had this problem and if so, how did you solve it?

Thanks,
Birman