They are pretty hardy. I think you’ll be fine because the whole plant isn’t wilting from that. I have actually grafted completely broken off branches right back onto the plant. With good success. Tape that up like suggested by Mike S and currdogg. Or just wrap/pull it tight with strings ( like kite string diameter string) so that they touch together as much of the wound as possible. Like how you would lash in arrowhead onto a stick with string, or how you lash the lead poles when you build a Teepee.The rest will scar up and heal.
If the plant isn’t wilting and the first tape seems good, maybe just do nothing more at all see what happens.
I know it was a different thread but:
you asked how to keep the plants smaller. I think doing lots more pruning while the plants are small before the stems get woody is THE MOST helpful to control size. Just remember when you prune aggressively, every time you prune you’re going to get lots of side branches. I’ve seen plants growing 20- 40 side branches after I keep them bonsai all winter with continual weekly topping. You just have to control all those side branches so you only have six or seven and not let the 20 to 40 grow. But that plant will stay nice and short. You could probably keep it under 12 inches (mini box grow technique) with the aggressive topping. Once they switch to flower the stretch is minimized relative to veg growth (some landrace or heavy Sativa crosses will keep on stretching anyway but not the hybrids that are most common).
And then more incremental repotting rather than a big pot. I Actually start in three or 4 inch pots, go to pint pots, go to half gallon, and then go to 1 gallons etc. Some plants need to go up to 10 or 15 gallon pots. Some do not need anything bigger than 1 to 3 gallon. It really just depends on the strain. Keep a log so you know how to to handle them next time. Grow log is a must if you want to improve growing!!
Once againI don’t re-pot until the plant starts to look root bound in the bottom. If I’m not sure I will even gently slide a plant out of a pot to see how the roots look. Even if I have no intention of repotting it right then and there. A vegetative plant won’t skip a beat growing if gently checking the roots. I do not recommend doing that to flowering plants though. I would not repot a plant that did not get the effects you first described in your initial post (deficiencies), especially if it’s ok in a 3 gal. I have grown many big trees in just 3 gal pots.
Lastly, put them out later. I have sprouted seed 2 weeks before the solstice that still get huge in smaller pots. The longer I grow I have been putting plants out later to have to top less (just lazy I guess). But then they are less likely to root bind or need repot or more nutrient feeds because they are younger plants. The only time I put plants out early (in April or early may) is to sex them early because they start to flower. (Sorry to tangent, that’s a different topic). You get the idea.