No worries, your doing fine. Remember this is backseed so you don't even know what they should look like Has the yellowing stopped or is it continuing to spread? Also, your going to see a BIG jump very shortly, your roots are exploring, one reason I put my riot cubes in solo cups or 1 gallon pots after they sprout is so the roots can't go too far, and the foilage keeps up with the roots. If you pull those plants up right now, even though they look so tiny, you'll find a very strong root structure, see how strong your main stems are?

These little ladies will be just find GM, your doing a good job. If your still seeing yellowing, increase your nitrogen just a bit.