It's normal for them to stretch at this point, it should be slowing down after about three weeks from the beginning ofn12/12 switch. Prepare to possibly support the longer growth shoots later, when they are surrounded with big, fat buds.
For now, maybe consider removing some fan leaves around day 21 of flowering, (it is not so important to hit that spesific day), to expose more bud sites in the middle part of the plant. Middle as in if you look at the plant from above 😊
First grow, exciting times... Have fun!
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