Good luck
I would just flower them out, and plan accordingly for the next run. It'll take quite some time for those plants to go back to veg. By the time you re-veg, then grow them out some more, then go to flower, the current flower run will be close to or even done.
Should I reveg? The middle plant is new there so I could get it a bit bigger.
If you only have a single tent, and not two separate ones, you might consider culling the plant you put in yesterday, and just leave the two that have been in for a couple of weeks.
The thing is, the 4 tips of the side ones already started budding. Will they Bush out or stay the same? If they won't yield much I'd rather let them go or risk reveg.
You should do whatever it is that you want to do. It is your Grow. We gave you suggestions. But it’s ultimately up to you.
Plants will continue to grow out or "stretch" for the first 3-4 weeks of flower. If you re-veg, you've wasted two weeks in flower, at least another two weeks to reveg, so that's at minimum a month down the toilet.
I'll see it out then and take this as a lesson
Where was the plant you introduced yesterday? In another tent? If so, I would flower out what you have and start a new round of seeds of clones. If not, I'd still flower out what you have. Re-vegging is not the answer.