I think you probably sowed them a little early and there still isn't enough light. Pinch them out when they get another set of leaves. Still plenty of time to sow more, days are lengthening now.
Is this pinched out or pricked out I wonder?
If you bury the stems slightly deeper in the compost when you prick them out that overcomes some of the leggyness-you can do this for some seedlings- but not all