I accidentally sprinkled ferilizer on my new grass seedling starting to grow > also watered it very good. Did i just kill the gras
seedlings were already growinh for about a week
That's hard to say without photos or description of the current condition. It is possible to fry new seedlings with excessive high Nitrogen chemicial fertilizer. If the grass is browned out and dead looking then you may have to start over. If it's green and growing then keep up the watering and hope for the best.