should I keep trying to mend fences

No. Anything - literally anything - you do or say now is likely to be interpreted negatively, particularly if it involves criticism of the MC or a larger role for you. Rule one of singers' nights & singarounds is that what the MC says goes - and that even holds if, as in this case, the MC is incompetent and hostile.

Is it improper to call on a performer met at this venue to invite them to another at a different place?

I wouldn't say it was wrong. It's liable to p*** off the MCs, but it's up to you how much you want to care about that. The real question is whether it's going to annoy people you don't want to annoy.

What is the best way to say that the managers blew the night for half of us...

Again, I don't know how diplomatic you want to be or why. If it was me I think I'd give a heavily-edited version of what happened, assigning blame as necessary but presented as a bit of a joke - "it was a bit more of a VERY talented player event than we'd anticipated... female MC had some interesting ideas about the running order..." - and leave it at that. If you want to tell the story without saying that the night went horribly wrong, you'll basically have to lie - and lying, you know, is a sin! a sin!