I don't think you can really install it badly.
As an update on mine. The log burner is working wonderfully. However when the chimney was being rebuilt something has gone wrong as smoke is somehow getting into the cavity wall at the back of our house when using the front room open fire. Walked into the back room and it was coming out of an air vent! No idea how it's getting in!
Isn't that a contradiction!!
That sounds like an absolute bad install.
Easy fix though. Sounds like you just need a flue liner