So, this morning I went to the store that supplied the valve body and trim, explained the situation, and that I needed another escutcheon to replace the one I scratched. The woman behind the counter went and grabbed an identical trim box off the shelf, cracked it open, pulled out the escutcheon and handed it to me.
This one had a square hole, allowing me to slide it right over the shower arm, screw in the arm, then slide the escutcheon to the wall and silicone the back. Easy peasy.
Long story short, it was the wrong part that was originally shipped.
Cost me a headache + 2 hours of screwing around yesterday, and now a 2nd trip back today.
Shake. My. Head.
I find these types of manufacturer/supplier errors are becoming more and more typical.
I am tempted to write an angry letter, even though I know nothing will come of it.
I suppose this is just the world we live in now. I wonder if these companies even have a quality assurance/quality control sector anymore.... Doesn't seem like it.