Ha! You have already figured out the #1 reason (imho) that people screw up their autos in the first two weeks. Cuz exactly what you observed. It’s very common in my experience. Took me a few to realize and adjust to that. Cost myself a week of growth a few times, which to me, with autos , means forget that one. Lol. I am currently allowing an exception for the 24 Karat, which on day 20 is not as big as your auto. But man has she taken off.Now she is growing! As if on a wild mission, she has suddenly taken off and is working on the third node. It will be time to top her before long!
Along with the slow growth, she was also not sucking up a lot of water. She was using a bit, but I can see where it could be very easy to overwater and overfeed an Auto just starting out. I patiently gave her little drabs of water every few days, waiting on her to finally drain the bottom the first time. She still has not accomplished that task yet, but I suspect that any day now, she is going to surprise me.
Now, the biggest plant in Veg Room #1, I give you my humble little Auto