You can try tying the large plant down and out. Go easy when pulling the branches into their new location, so you don't break the stalks.

Remember this next time and try to time it better. I would estimate that the height/volume triples after dropping the light to flower.

I'd probably just grow on 4 corners, next time. I'm not familiar with your setup, but I've been doing a 4-corner thing for a long time and they always fill up the space. The light might be split more efficiently, that way.