You can regulate the Space between the Nodes with your Lightdistance
If you rise your Light the light gets "diluted" and the plant stretches for the light
If you get closer, the Plant " dwarfes" under the light. that is what i see here
Top leaes look alittle burnt to me too
Iam growing with the SF-1000 too... My plant have in the beginning adistance of 75 cm... those Quantumboards are very powerful.
Just give more distance, and you will see in a few days that the Plant stretches