Yes, in hindsight this would have been a better plan, and I did consider it.
My initial reasoning was that the parcel tray needs to be screwed down on the ends and I didn't want the screws visible. But it would have made for less wrinkles in the end, and a much easier install.
If the wrinkles prove to be too much of a deal breaker, I may take it out and redo it in this fashion.
Somehow, in my addled brain, this seemed like the "easier" way... 😅