@JarJar it’s pretty normal for that to happen until you get the hang of it. Either way though she’ll heal up and get a knot. You just want to make sure you keep her wound clean so she doesn’t get any pathogens inside.
You are correct that it’s only supposed to snap the inner hurd but until you get it down breaking the outer is bound to happen.
I’ve taken branches clean off myself before I got the hang of it.
It helps if you massage the fibers in the branch first. Warm and soften the outer so when you twist the inner hurd breaks and the outer just flexes a little.