Hi,
Someone more knowledgable will be along shortly. But what do you mean by its almost an octave high at the 12 fret? do you mean the intonation is almost right or that it's an octave higher than it should be?
The distance from the 12th fret to the bridge will be slightly longer than the distance from the 12th fret to the nut to compensate for pressing the string down onto the fret making the vibrating section of the string ever so slightly longer than half the length of the unfretted string.
The experts will provide guidance but it's the weekend so you may have to be patient.