Leaves are turning a bit black/black dots/black on a corners of leaves

Dark spots or black edges on leaves can come from a few things, but the most common causes are: Nutrient imbalance – possibly a phosphorus or calcium deficiency, especially during flowering. pH drift – even a good nutrient mix won’t be absorbed properly if pH is off. It’s worth checking runoff pH and EC. Environment – cold nighttime temps or poor airflow can cause leaf stress and discoloration. It doesn’t look like a serious issue yet. If the problem isn’t spreading fast, you can likely correct it by adjusting your pH and checking nutrient levels. Keep an eye on new growth – that tells you if things are back on track.

You already planted like you have so it's done. You want a fix. I have done this: fed 1 liter of 7ml per gallon Big Bloom, around the drip ring of the plant. Just one time. Plant likes it, gets happy. A week later the same but 30ml per. She was off to the races. It's organic, mostly guano but so much more. Look it up and see if you have something like it in your toolkit. Can be used on seedlings.

Plant looks like its starving. either for nitrogen or light. or even too much light. something needs to change though. the plant shouldnt need any nutrients right now unless its older than 3 weeks? but she shouldn't be so

Would you take a 5 gallon pot, fill it with soil, put a single carrot seed in it, then mulch it, then wait for it to grow? Watering that would be hard. Any issues this early I'd imagine relate to watering/container size.