You are saying you got these seeds in a kit? That they were labeled Black Pine? I wish they had given you better instructions. One never plants seeds in Bonsai Pots. There probably isn't even a hole on the bottom?
Your soil is way too wet. You will probably get root rot or rot of some kind before this seedling is able to get much older.
Seeds need to be prepared for their individual needs. Some need paper towels and moisture, others need refrigerated, some need to be blasted with flame. You've actually got one growing! I would get a tiny peat pot not more that 2" by 2", fill with potting soil and using a spoon transplant this guy into a small pot where it won't be affected by too much water. No drainage and then no root mass to suck up water is a death knell for that plant.
Bad instructions! I am sorry. You still have ONE that is viable. Keep a bit moist but NOT SOGGY. Allow it to dry before watering. Use distilled water, not tap water. Hopefully you are able to find distilled water without fluoride.
Potting soil, small tiny peat pot for now, and what are you using for light? It needs light now and your seedling should start looking like this picture I am sending. Fertilize only when it gets 4" high. Not now. If you use Osmocote you won't have to fertilize again until you transplant or up pot your seedling. Use very little! A pinch until you get to a 6" pot then go by the directions and only do half of what the instructions tell you.
Black Pine Seedling