I often used to have difficulty with seeds. I frequently planted three or four in each spot in the hope that one of them would germinate. Do you slugs, birds or squirrels eating them? I once tried germinating carrots inside the house but when a carrot starts to grow, it sends down one 20cm very thin thread, which eventually grows into the carrot. So when I transplanted the seedlings into the garden, they grew into corkscrew shapes.