what you need to do to fix that and make it stronger is transplant into a bigger pot. transplant it so the dirt comes up to just below the round leaves. This will take care of the stretch and make your seedling stronger. Keep a fan on low just so the seedling flutters in the wind just a bit, this will help make it stronger as wind triggers the stem to get thicker. Make sure that you keep the lights close enough so it don't stretch. If using flouresents or cfls keep the light a couple inches from the top. Dont use HID lights until it has its first set of 3 point leaves if you planned on using one of them in veg. You dont want to burn the little one. Let your soil dry out before you water so your roots can grow nicely. Keeping the soil moist all the time stunts root growth and can cause root rot. Dont feed it any nutrients until its about 3 weeks old as seedlings have enough stored energy to last them the first 3 weeks or so. Hope all goes well. It looks very healthy besides the slight stretching.