I'm having the same problem with mine. Its my first plant and I'm not positive but my best guess is that its still concentrating more on root growth than actual stretch. If that's the case then its actually a good thing and probably nothing to worry about. Im told once the roots are more developed the plant will take off and gain more height.
If that'a a blurple, turn on both switches. I've never used one personally, but that's what I hear all the time. After take pics with the light off comments, lol.