Update.
On john's advice, I went ahead and ordered the ardex 8+9 for a little insurance. Very nice product and mixes well in small batches with the OL's sunbeam handheld mixer.
Glad I did.
The stuff rolls on kind of sticky as a second coat. So sticky that in one area it actually started to pull the kerdi away from the drywall.
This was one of the first wall pieces I installed. Being a newb, I made two mistakes. First off, I tried to use large sheets around corners. Bad idea. They use smaller pieces on individual walls for a reason. It is a PITA to try to go around inside corners. Outside corners seem fine. Second mistake was using big box store Mapei thinset to begin with. The second bag was mapei from my tile dealer. Night and day difference. Same price. The more I shop at real stores, the more I loathe Lowes Depot!!!!
Sure wish I could backup a few months and do this damn job the old fashioned way, using cement board. The way I originally intended to do it before I let a Kerdi salesman get ahold of me.
So, where do I go next? Do I consider this a rather expensive lesson, rip it out and start over with CB and ardex overcoat? Or, do I assume that I did a decent enough job on the rest of the kerdi, repair that section and tile away? The rest does seem to be adhering well.
To repair, my plan is cut away the bad section, install new kerdi and ardex over it. Is it possible to cut out a section which is about 2 ft square, clean it off and reinstall? I am out of kerdi. I actually was able to return the unused half roll, contrary to what some said. I do have enough band left to seam it.