Sow them later, they will more than catch up.
Also...only sow one of each plant so that you can give them the space and light they need. To get more plants, use the armpits [leave the bits that you would normally pinch out until they get to two real leaves] and plant them up to those leaves to make new plants. They will flop for a week and then grow new roots and continue to grow and give you new plants.