Hey Greenfingers,
I am a noob at this but i'd like to help if I can. Check out my grow for pics, IMO experience I have just went through the same thing with my girl and somewhat still am and shes in her 6th week 🤔. Genetics and strain could be one reason as I have 3 plants growing and only one of them stayed short. Stress of some sort will be another reason such as low RH and temps. 35% and below can keep growth slow and steady but short and stout. Speaking of stout don't let fan blow ON them yet as they will stand their ground and yes it makes stems strong to do that BUT your plants will be defending themselves against this wind and stems will widen instead of lengthen keeping it short. Put fan blowing in between light and canopy. Feed them some nutes I believe they can handle it at this age just keep it light dose untill 3 weeks old. I think you should take your light as much as 32"+ and get your plant to reach for it. Dont know your setup in whole but your plant is actually much taller than mine was at that age. Mine in 6th week is just in last 2 days started to rise up and show her cola potential. I hope I said something that makes sense or helps😎
Happy Growing