Although I made the decision some time ago, when it comes down to it, picking up the rotary cutter and slicing out a chunk of a half-finished quilt top is a daunting prospect!
Using several large rulers (I absolutely love the 18in square I bought a while back, it's invaluable!) I carefully marked the section to be removed first, to make sure it was totally squared. Then I bit the bullet and cutI Then I carefully measured the gaping hole left behind and cut a new centre, 1in larger in either direction.
I'm not going to put the green 1/2in border again; I think it'll work better without. The new centre isn't attached yet, but I have traced, fused and cut-out the new tree; it's much bigger and in some darker, wood-print fabric.
It feels good to have made the cut and be making progress again.