don't try to force it... It looks fine.
your lights and the genetics are everything.. read plant and react.. if you've been feeding since seedling, lay off for a bit before a problem arises. otherwise, once those cotyledons show a little fade, you can begin a regular cycle of fertilization.. observe plant daily for changes.. take a wait and see to deduce problem fully befre adding things. always easier to fix a deficiency, than to fix the original misdiagnosed problem plus a new one.