Your stem stretched initially so I would add a little more dirt. It will give it more support. Also with fluorescents you want to try to get about 2 inches from the tops of the plants,and 77-78 degree F is optimal temperature for photosynthesis. Arjan from Greenhouse seeds used 25 celsius in the day, 19 celsius at night ( 77F, and 66F ) This isn't a necessity to do a temperature change, just thought I'd let you know what the real connoisseurs maintain in their grow rooms. Good luck