Relax, everything is fine. The plant looks healthy and even stretching a bit, if that didn't happen initially, of course.
You have a small plant in a large pot. The tap root is the focus right now. It's going to be slow until it hits bottom and fiddles around a bit before it figures out there's no place to go... then, the plant's going to focus on above ground growth more. It'll average out over time, roughly, if not a tad slower, maybe? You won't tell a difference by the time it's all done filling out for 12-12 or if auto simply blooming. it's an auto.. just give her a second.. the pot size dictates height, and that's a 3-gal? 2-gal? she's gonna get full-sized.
small radius around plant as you do now, it seems. Slowly increase. Because you can't rely on runoff, you willneed to account for evaporation with some ph-only doses of irrigation occassionally, or it may build up where roots do not exist... difficult to get teh benefit of a 20% runoff if not watering entire pot, which you can't do yet without other issues from that.
+2 strains
