Re: a teaching mistake
Things like that happen, and not just with advanced techniques. No big deal.
I would remain with that uke and try to solve it, even if it takes time, because that process is also very interesting for the students to watch and learn from.
You can do it slower, and even guide uke to the response you wish for. It doesn't have to work perfectly the first time (or any other time, for that matter). It is very interesting to involve in the process toward perfection.
And I do believe that every teacher needs to explore her or his limitations, even when it means making mistakes in front of the students. As long as nobody gets hurt.