is the plant outdoor?.
its very small for over 12 weeks of age, it could have been vegged and flowered in that time, but outdoors takes longer.
i have 3 growing outdoor"in england" and mine are 2 foot tall and all topped"16 main colas/tops.
i feed mine every 4 days , and if you havent fed your plant before, then do, only half the rec dose, for the 1st few times then grd take it up, to the rec dose on the bottle.
also i would pot it on, it maybe root bound, and thats why its soo small, or not getting enuf light.
it looks sad, maybe put it under some flos for a week or two, to get it going.
are you growing outdoor?
have you fed it yet?
and like i said repot it on.
is that your only plant?.
btw welcome to the site.