Leave it alone. They do not respond to pinching. they do best with a single stem that is supported by a stake. Allow one flower bud per set(pinch the two side buds which appear and are singles). Hanging begonias will have multiple stems.

Non stops usually grow quite bushy without any help in my experience

There are some non-stops that will grow to very tall heights. I had one last year that went to 3' before it broke. You should focus on how to stake begonias. Pinching is not effective for these plants.