tall seedlig after mistakes

how do i fix mistakes in hydro, 1st time grower. its about 3" tall

put it in dirt. haha

I had that issue as well. I didn't expect the seedlings to pop out of the rockwool so soon, so I hadnt turned on the lights.
The fix is to bury the stem when you transplant it to your larger net pot. Otherwise just bury it deeper into your medium if you are not going to transplant.
After a period of time it will create roots and you have a lower plant