Sometimes autos do odd things. I would not top now as she is in full flower. The good news is the plant will put all its energy into one nice big bud!
I agree there with @Riskguy not topping and auto’s genes. I wanna add for you, a few reasons it’s stunted. I’d assume the roots didn’t develop into much. Either a transplant problem, a compacted-soil problem, or overwatered. You’ll find out when it’s done and dump it out if it’s root ball is small as your fist or half brown and rotted.
Or low energy but you know if it got enough light throughout it’s life.
Maybe faulty genes and it was fate . I hope you figure it out and good luck growmie
