is it an autoflower? it's supposed to do that.
if it isn't an autoflower, then you have given it 10 or more hours of uninterrupted darkness. that's the only way a photoperiod plant can switch to flower phase.
That looks like it is pistils at the terminal bud, so we aren't just talking about preflowers, which can show up in vege phase.
It's also possible the seller mis-packaged something. If you are certain it is supposed to be a photoperiod, and you did not change the light cycle, then they put soem autoflower seeds in the wrong package.
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LST / plant training
it mostly helps reduce proportion of larf buds. it doesn't increase yields. so, train as best you can for a level canopy but it's not the end of the world if it takes you a few grows to figure out a good procedure in this regard. trial and error. Breaking apical dominance is a simple cause and effect manipulation of the plant. Bend something down and taller portions of plant will take more resources and grow more. sometimes you want to permanently tie something down, sometimes it can be temporary.