Glad you didn't have your heart set on them. I've lost plenty.
There's a reason why each plant makes thousands of seeds to replace itself- funny, but think about it...
Potting mix should be fine, it's just topsoil that would be too heavy.
And probably spraying while the seeds are still not showing- keeping the soil moist to the top. I cover lightly with plastic. Shortly after you see green, bottom watering works well for me.