Kane - easy fix - you got any StewMac superglue? I'd say not your fault - more to do with how fragile the end of the neck is and how much glue they use to hold the nut in place. All it needs is a touch of superglue and Bob shall be the relative of choice. Titebond should be OK as well - when I've been with Gav and the same thing happened (twice) all that's been used is a tiny amount of superglue and then some light sanding once it's all finished.
Don't worry about it though. Easy fix and you'll be the only one to know once its all fixed.
EDIT - all I meant was to fix the wood - gut feel your Tusq nut should be able to go in as per plan once the head side of the nut is fixed. Shouldn't be a biggie and should be straightforward to fix.