You might wanna plant more than one new one.

The others may have also suffered enough to sustain damage that you dont yet see. Like, stunted growth from here out.

The seconds set of leaves will come once the first set has allowed the roots to stabilize and the tap root is well developed.

It could be as long as 7 days on some poor overheated and streessed out seedlings....

Get a real light.

People who use HPS during veg cycle will get some stretch, but usually its bright enough so that it still provides ample light even though its distance from the plant is extended.