So that's bronze?
the bb shell has the advantage that you can tell if you got penetration by looking inside. What does it look like in there? Unfortunately, it looks like there wasn't quite enough heat to get good penetration. OTOH, it's not burned to a crisp, although you overheated a spot up the seat tube a little.

I'm always a little surprised that people don't practice on pieces of tubing. When I'm doing something new I practice with tubing and I've been brazing since the mid-'70s. .058 inch wall tubing is a decent slip fit over the next 1/8" smaller diameter tubing. So much cheaper than parts.