its only" safe" ina loose sense of the word if you cant smell the fumes in the cabin,kwikshi7 living up to their useless reputation,get it sorted soon as you can and learn from this that "you can get better than a kwikshi7 fitter,we're the boys to distrust" if you can smell fumes from within the car then dont drive it and when you do return it to them,drive with windows open to ensure ventilation,plus demand a discount for your wasted second journey and time on a matter that should be a simple procedure.
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Go and have it cheked asap, meanwhile drive with the windows open.