From a fellow grower: The leaves in question are the 1st and second set they have been in flower several weeks in the original pictures they started flowering in less then a week of veg they now are 2 1/2 to 3 inches tall they will not get any bigger I’ve never seen this before.
Watering schedule is same for all every 3 days unless soil is completely dry.Soil ph is 6 water ph 6.4 soil is Coast of Maine organic natural growers mix.Coast of Maine organic nutrients 5-2-4 dressed with worm casting bio char and natural amendments.
Average day temps between 76° and 78° at highest humidity 55-65
Vpd day .85 night 1.5
4x8 tent 4 spiderfarmer 2000sf leds total of 800watts side lighting ac infinity bar16"evo lights total of 8
Ac infinity uv 12" bar total of 8.6 inch intake 8 exhaust 2 oscillating fans at each end
For these seeds followed the information on speedrun site to the letter soak in water till crack and put into paper towel once tap root shows to prevent drowning, my last ditch effort is to put them in soil to see if eventually pop and eventually have to throw away small solo cup with soil and seed because they usually became contaminanted and mush followed container size with containers 7 gallon fabric pots and starting them in them with organic super soil and organic nutrients.
Been growing since my teens and have gone from special florescent tube before t5s to warehouse 400 watt metal halide and high-pressure sodium to ones made for cultivation then to Cmhs and then blurple leds to now quantums and bar lights
Light schedule is 18/6
As to your question “will this Auto flower get any bigger”.
Stun Auto flowers are hard to determine until after the stretch. All I grow is auto flowers and I’ve noticed the majority of stunned autos after the stretch determine (for me) whether or not to keep them or to start over.
In my experience, if the stun Auto shows promising growth and has a height of at least 11 in a week or so after the stretch she’s worth keeping. I’ve had it happen several times and the yield is approximately 1-1/2 oz to 2 oz
If the stund Auto shows a struggle in growth and maturity I start over.
As to the coast of Maine it looks as if you’ve started amending the soil. Since amending if the yellow doesn’t clear I would add some calcium magnesium (Cal mag) in that small of a plant maybe 100 PPM of calmag per gallon.
Your temps are on point but I would raise the humidity about 70% for a couple of weeks.
Autoflowers are incredibly sensitive during seedling and vegetation stage. It’s very important to be on point with your environment, you’re watering, and feeds as the least amount of stress during these stages can lead to stunt growth and premature flowering.
It’s difficult to say what could have stunned your plant. They’re just so incredibly sensitive and unforgiving to stress during the early stages.
I hope this helps a little bit. Good luck to you
What day were the seeds germinated?