Stems of my autoflower

focus on the new growth. that stem will thicken up. if it stretched early it's not something you can undo. you can bury it a bit deeper to shorten it up when you transplant. Don't go too extreme on this, but it can mitigate a little early stretch that can happen to anyone. light is the key.. too much it stunts growth completely or causes too little internode growth (sometimes takes days for the full negative impact to be felt). too little light and it stretches. Watch new node growth. that is your guide. take some notes as to how you ramped up to meet a seedling's growing needs. try to pre-emtpively follow that path next time. seasons may cause some variance (temp/RH = VPD, or maybe furnace adds a little co2 to the area, etc) as can genetics, but most will want roughly the same things. if necessary, use a toothpick or something similar to prop it up / support it. They are so delicate at his point it doesn't take much. I just folded over a piece of tape at the top and used that to rest plant against. no tying or wire etc. just leaning on it is enough.

Just a little too long, she is not really streching. Now just provide her with a little more light and use a fan that blows the young plant gently. They will develop a thicker stem when you do this!

Terp1 has nailed all the options you have.... pick one and take his advice!

Nothing to worry about at the moment. Slightly increase the light intensity or hang your lamp 5-10cm lower. You can also bury the long stem deeper or fill the pot with more substrate. It will also root. Good luck and a bountiful harvest. 😎💪