I over did trimming a wax myrtle, I had permission to do it, the plant will come back, however, am I in trouble, My neigbhor wants its so it can be like a hedge but it grown out of control .
Is there a question in there?
Is it still a hedge...Or did you trim it so much that it is now a small shrub? I think you know the answer to "am I in trouble," since you said you over did it.
You could always offer to glue the twigs back on.
Kidding, of course, but it illustrates a point. Whether you're 'in trouble' is between your neighbor and you. If they gave you permission, it would be pretty hard for them to sue you for the cost of a replacment bush. Said replacement would probably be no bigger than what's there anyway.
Apologize and move on.
And vow to discuss fenceline projects in more detail next time. :-]