I can't find a preflower of any type clearly displayed in any picture, so ensure it doesn't have any sacs/grapes hanging out to eliminate possibility it's a male.
Is this an autoflower? Occasionally, the genetics just don't match up... less often with reputable breeders, but even they can have an autoflower-dude, so to speak... if that is the case, give it 12 hours of darkness each night and treat it like a photoperiod. i'd get that plant a bit closer to the lights if that's the case too, since 18hours (or however you normally run autos) is likely not as intense as you'd want for 12 hours. Need 33% more intense light to provide same DLI over 12 hours vs 18.