Should I transplant the 3 gal into a 7 gal? Thinki...

7 gallons a bit too small jump, go closer to 3x previous pot size.

If you want to let her keep growing i would get a trellis net to controll the sideshoots and branches. I don‘t know how stable this groth is but it seems to hold on. Maybe you can start training because otherwise you will lose controll over the form.

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Due to indoor lighting, you want the plant reaching these heights in flower, not vege. your light, even if very strong, will only be effective 18-24" deep into canopy... side lighting and such would do more, of course. i wouldn't do much with that info today, but in future grows consider the dynamics of indoor light sources. in 3 weeks that thing, if not restricted by pot or other factors, will be 2-3x larger... then another 2-4 times larger than that after flipping to flower scheduel before it stops growing. your plant could be 10x larger or severely rootbound and sickly. I don't think either is exactly what you want? i don't know what your goals are here, but nex time start by working backward from what you want at the end of flower stretch. this will help with logistics of how long to vege and how much to train, how large of a pot ... etc. imho, i'd take the top third off and start traiing the remaining horizontally and flipping soon. create a more level canopy with 'enough' branches going vertically and flip it to flower. a plant can only provide for so many "mouths" before topping and training doesn't add any more weight but rather creates excessive proporitons of larfy buds. 2-3 colas per sq ft will do you good.... better than 10 colas per sq ft... your pot size, nutes , light and other environmental factors will dictate how much the plant can provide for. lots of variables that are different in one garden to the next.. ltos of methods that are less optimal than others...