Please help

If that’s an auto and 3 weeks old, I’d figure out how to keep my temps adjusted from fluctuating so much and start over. The problem is in the root zone here, they don’t like staying soaked or cold. Autoflowers will not do well when faced with delays in growth.

Without any real info, it is almost impossible to give a helpful answer. Overwatering is a very common mistake with new growers and that is often the reason for stalling small plants, but it could be a number of things.

Missing people's phone calls is not cool

You dont wany a big change in temp day and night only. Example. 26 day 21 night.. Don't go less than around 18.

Definitely too cold at night. And, better if it's slightly warmer during day, but at least doable at 20c. Think your light is too close/too intense at the moment. Back off until the internodes develop a healthy length between nodes. You'll probably need to amp back up later as it matures, but for now it seems to be getting a bit too much... could be related to the colder temps, too.