Need help with cutting last border.
 

I have a quilt top. The center panel is appliquéd and there are 12" Sawtooth Stars blocks around that and a 4' border. When I measure for the final border I get 86" x 79". But when I measure across the center of the top I get 85" by 78". How do I cut my last border? Or do I try to cut off the first border to make it square? What are my chances for this thing being flat? This quilt is my daughter's wedding present and I'd like it to be a perfect as possible.

It appears you'll have to do some minor 'easing' of your top. One each on each side over those lengths is not much to ease in my opinion. Are you using cornerstones in your last border? If not, you'll have to attach either your sides or your top/bottom and re-measure to account for the borders you've just added. I would probably cut my sides the longest length (79"); find center of border piece and quilt top and pin to each end from the center. If it looks too puckery (is that a real word?) chop off that extra inch and re-do the pinning. If you're willing to rip that stitching out you might get a better feel for how it will truly lay after stitching vs just trying to visualize while it's only pinned.