Those necrotic margins make me think it’s a K deficiency. I don’t grow weed, but I’ve got a soils background and nutrient deficiencies are a secondary skill.

What kind of fertilizer did you add?

How deep is that pot? To me it looks way too large for a tiny plant. I assume by first time grower you mean you’ve never grown any plants, cannabis or otherwise.

The worst thing you can do to any plant is to overwater it. When a plant is in a pot full of soil and its root system is very small it cannot absorb water quickly enough from the soil to prevent anaerobic conditions developing in the root zone. Anaerobic conditions cause root rot which will stunt and eventually kill a plant.

It’s much better to have a small plant in a tiny pot than a small plant in a giant pot. A plant that has overgrown its pot will demand more frequent watering but is not in danger of root rot. Plus it’s much easier to transplant a plant with a dense root ball than one with a ton of soil but sparse roots.

Anyway you should check the bottom of the pot to see if the soil is waterlogged. If there are any bad smells emanating from the soil at the bottom then you might need to do an emergency transplant into fresh soil in a smaller container, ideally with lots of perlite in the mix to promote drainage and aeration. During the transplant you’d want to remove all the soil from the roots and even rinse them off to get them relatively clean. Any roots that feel soft, dark brown and slimy should be pruned off so that only firm, light/white roots remain.

@j_roby@slrpnk.net help this guy out.