What am i doing wrong?

I am concerned first time trying to grow and this plants almost 3 wks what am i doing wrong thats causing my leaves to yellow or if its burns. Please help with instruction id deeply appreciate it. Thanks

New growth looks okay but more information on what soil, nutrients, etc. would help.

Other than that looks like you're stretching and the stem is pretty weak.. Curious what kind of light you are using and if any fans on it.

i do not have any fans on it, its just potting soil no brand name, i water, and then ever 2 weeks mirical grow i feed, but also keep in mind i really and just going by what people tell me and what i see online. this is a weird batch of seeds i got idk the strain or anything but i ordered good Fem seeds from herbies and before i ever plant them i want to get these down on how to grow and fix problems
the LED is a UFO 150watt LED i am upgrading to a 600watt very soon LED or should i get 1000watt? im just wanting to get the happiest plant i can and for my first its def exciting to see it grow but now im like oh man. lol

Ok going forward I would look into a better medium like fox farms or even pro mix. As well I would stay away from anything miracle grow for feeding cannabis. I use general organics for feeding but there's lots to choose from.

Are you in an enclosed area? Usually important for maintaining a stable environment. I would look into some cheap desk fans and a carbon filter or something. The light you want would depend on how much space you have to work with. Right now they are stretching cause not enough light/too far away and you need some air moving on those stems or will run into issues down the road.

Think if you correct these things you'll be in ok shape for next round..