You need to be in a gal pot atleast.
You want 1gal per foot of growth.
You can bury the stem up to the 1st set of round leaves to combat the stretching.

You want the hps within 18".
As close as you can get it without burning.

You have not said anything about ferts (may have I do not recall).

You should add ferts at 1/4 strength after 30ds from seed.
Also you want to feed them and let them dry all the way out before watering or feeding again.

Ventilation is imparitive for plant health.
Ideally you want the air in the room to exhaust itself within 5 minutes.

Looking pretty good so far.
With a little learning you should do very well.

Happy growing