Screen replacement: Forgot a blue liner

I can't see anything obvious that would give you problems if you leave that piece of liner in. As a veteran of a lot of phone repairs, including Pixels and iPhones, I'd frankly leave it well enough alone.

My concession to responsibility would be to go ahead and order a replacement precut adhesive sheet to have it on hand should it finally get to bugging me enough that I finally decide to open it up and pull the liner. But yes, you would have to go through the whole screen replacement procedure again just to take that stupid piece of plastic off; even though the chances are small, there's always a chance of damage to the screen when it's removed, and as such I'd say it's not worth it.

Just my thoughts; take them for what you paid for them! Good luck and let us know how it all turns out for you. Whichever way you go, it may well help the next guy who comes along and does the same with their phone.