I would move it outdoors for summer. Bright light, warmth, and humidity makes a huge difference.

Here is mine from years ago when I grew it from the nursery on our front porch (Atlanta area).

But if you had a public greenhouse (Atlanta Botanical Garden) then you could grow it to 12 feet tall or taller. Here is their giant earlier this month.

The begonia in front is obliqua and about four feet tall.

Wow!! Thank you so much. I had no idea they could get so big. Yours looks amazing! I’m going to put mine outside right now.

Don't put it I full sun but I am sure you are aware of that. Acclimate it to begin with just like getting a tan instead of sunburn.

You can cut your plant waaaay back to reshape/regrow it to a fuller specimen. Make cuttings from the cut stems.