Dont worry about PH. if your soil was acid or alkaline enough to cause a problem you would see pale yellow leaves and stretchy thin growth.
your plant looks real healthy, but real small for early march planting.
Heres a few issues. early march is BEFORE the vernal equinox, so it experienced ~12/12 day cycles as a seedling, then you put it into flower after a month or two of lengthening days. most likely it is confused as fuck and has been trying to transition from seedling to flower to veg and back to flower. I never put out photoperiod sensitive plants (most varieties of strawberry, and a few garden herbs) before the equinox. those few i have put out early always have slow ass growth for the first several months, as well as odd life cycles (my mother's too early basil has already gone to seed, in may!) dont smother your plant with the pressure cooker of those plastic bags. get a big cardboard box, and paint the outside white. use this to dark up your plant for flowering. I doubt your plant has even figured out what it should be doing yet. keep a steady light cycle, and hope it gets better. thats all you can do.