first we need more info.
what kind of water are you using tap/RO/well water?
what nutes are you running and whats your ppm/ec at?
what lighting are you using..CFL/HID/LED?
it looks like you have more than heat issues going on..like way to many nutes or your ph is way off..ph should be around 5.8 to 6.0..it will go up and down depending on how its feeding.
do you have a ph meter and a ppm/ec meter?
although some use a feeding schedule..which works for them,but i can't see getting by without a ph meter.
after 3 weeks of vegging you should have the makings of a decent size bush..so yes somthing is wrong,but you came to the right place as there are many experienced growers here to lend a helping hand.