Your soil is totally wrogn for cannabis. You gotta run it at pH 6.7 or so. That's the problem, and it's worse from overwatering in low light conditions.
Choose a normal potting soil like promix. Unless you REALLY care about those genetics, that's a do-over- that plant may never grow properly because of the stress and stunting it has been subjected to.

Read the first link in my sig all the way through, and practice on bag seed.