Yo, your seedling looks stretched, I would re-pot and put more soil around the stem. Whatever light you are using get it closer and swap the tin foil for something else! Not having a go at you dude but your plant is very small for 3 weeks, maybe it needs more light. At least you posted while your plant is young and you have a bit of time to sort your grow out. Good luck
Oh yeah,you gotta do something about your lights,you need more & move closer, Get rid of the foil to,
Could you tell us a little more about your setup so we can try and help... Your plant is not exactly what it should look like at 3 weeks. Lighting is probably the cause in this case, I only see one reflection.
What kind of light are you using / wattage / distance... it for sure can be turned around, and then strecthing can be resolved once its time to transplant.