Would flush well with ph'd water, and don't offer nutes till 3rd or 4th set of leaves are showing. If it's been 3 weeks, and it looks like that, I would likely start again. I would keep trying on that one tho. Any experience...is good experience.
Also, It's pot is too big for such a small plant. Next time, would wait till you want to start feeding her before you transplant.

Supersoil isn't the best, but is workable. You'll need to add perlite. Keep in mind that it already has some nutes in it, which last about a month or so with a vegging plant. Can make germination a pain if new to the soil, too.
Rusty Trichome Reviewed by Rusty Trichome on . What am I doing to my plant? Here is a pic of my new seadling. The tip of the new leave is brown. I am watering it a little bit once a day. It has been this size for over 3 weeks. I am worried. Rating: 5