I don’t think you over grew, she just got big! It’s an auto so they can sometimes do what they want and you can’t train or defoliate as much to slow them down!
Do you have some magnetic hooks you can use to tie all of those main top colas towards the outer rims of the box? You’re gonna wanna just try your best to keep them away from the light!
Another method of training is called “Supercropping” which you may have to do to save your best buds!
Overall, that looks like a really nice plant with a good amount of main branches! How far along are your flowers? Hard to see from the pic 
I know the plant seems super tall in a Grobo but realistically that’s not that large for a Cannabis plant, so they can easily take up all the room you give them… Lots of people have succeeded in a similar situation, you just have to use some crafty techniques to keep those colas out of the light as much as possible and secure them.
One plus side is I think she might be done stretching… hopefully… so if you can work with the height she is now you can succeed no prob!
Genetics has a large role to play in the height of a plant, and it looks like your grow conditions and such were on point cuz she thrived
Thanks BIG TIME Let me try the BEND!
You might be able to just lightly bend also and secure them to a tiedown from a magnetic hook to the branch itself, might not have to fully supercrop at a 90 degree angle type of deal!
So i am on DAy 76 overall 38/50 of flowering… Yeah i just used the things to put it on the side.
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