The stretch is because the light being used not really powerful enough causing the plant to reach for the light,or the light being used is too far away causing the plant to reach for the light.
If it continues to stretch now that you have moved the light closer then you need a more powerful light before it bends over and snaps under it's own weight.
The fucked up leaf problem is because you're growing from seed in Hydroton pebbles and giving a delicate seedling far
TOO MUCH WATER.
You need to be raising that seedling in just the rockwool cube with minimal hand watering until it has it's first 2 nodes or so and then transplant it into your pebble hydro system with much less water,the regime you are using is suited to full size plants. You only need to keep the rockwool cube moist and with a seedling that small if you put it into a humidity dome in my experience it would take around 4-5 days before you would need to moisten again.
These are a couple of mine at 20 days old from soil break in half pint party cups,yes they are in soil but even so they have only been watered 3 times in those 20 days.
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