There are several reasons for you (which I have also experienced):
1. It's too cold. At least 15 degrees in the dark, 20 degrees plus x during the day
2. Lighting time for short. Increase to at least 18 hours, 20 hours is better (some swear by 24-0, but the electricity costs are too high there)
3. Hang the lamp a little lower, or you are using the wrong lamp (I can't tell from the diary)
But the good thing is, your plant will also flower later, so you don't have any disadvantage (apart from needing more time).