I wanted to update everyone who so kindly helped me with my triangles.
I resewed the first column, finger pressing each triangle center and sewing the opposite way on each seam. I ended up with the same slant problem, but this time it was immediately clear to me what I was meant to do -- tilt the slant back to vertical and even off the top and bottom! I'm sure if I'd posted a picture of the slanting column the first time, someone would have understood what to do. The lesson for me is, a little patience can save a lot of work. I think if I had just walked away the first time and slept on it, rather than impulsively cutting, I probably would have seen the solution.
I have laid the applique pieces on the surface just to give the general idea. I must set this aside for awhile now as I have a couple of other hand sewing projects ahead of it. It occurred to me that the trunk was a perfect opportunity to try out the Ruth B. McDowell piecing method in a limited area, so I pieced the trunk, making it a little wider. I also changed the bird positions so as to get my birds in the lightest areas possible, so they would show up.