The strands along with the core of the yellow wire need to go correctly under the screw also, basic stuff needs a bit of practice.
It also looks as though you have nicked the yellow insulation.
Well, I've been an alarm engineer for as long as I can remember and what has been suggested, especially the first answer is the way to go.
J, what do you think should be done then?
Please put me and hundreds of others right then.
It is an offence not to say who the driver of the vehicle was, surprised it did not go direct to your employers (or have I got this wrong and you are self-employed?