Answer: How frustrating! Based on your description I am not certain what happened. In general you would start them about eight weeks before you expect to plant them in the garden. Provide bright light such as two ordinary fluorescent bulbs in a "shop style" hood with the bulbs just a few inches above the foliage; run the lights about 16 hours a day. (A window sill is not bright enough.)
Use a good quality soilless potting mix formulated for container plants. Water as needed to keep the soil damp like a wrung out sponge, not sopping wet and not dried out so they wilt. Fertilize weekly with a water soluble fertilizer such as 10-10-10 plus minors at the weaker strength listed on the label.
Thin the seedlings and/or transplant to one per cell or pot as soon as you can tell which ones are the most vigorous; this prevents them from becoming crowded and stunting each other. You may need to repot them into larger individual containers as they grow, do so before the roots become crowded.
Grow them at a cool room temperature, 65 degrees or so. If they are too cold, they may slow down. I hope this helps you trouble shoot.
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