For a wing that tapers in thickness and in planform, yet uses a constant thickness jig spar, you’ll usually find it is not parallel to the main spar nor to the TE.
What I’d suggest is that you determine the position that gives a level root rib, then determine the position that gives a level tip rib, and fix the jig spar to the building board so that it goes through these two points.
All ribs in between root and tip will now be correctly aligned.
Just make sure you have the exact mirror setup for the other wing panel.