If you're able to trade without the proper margin, run don't walk as far away as possible from that broker. Some other joker can do the same thing and guess who's funds go into the kitty to make it all right?
The broker won't bust the trade because that involves the exchange and the counterparty. But I believe they have the right to take your profit and add it to their error account. If they think you did the trade intentionally, they would be more likely to do that. But they could also conveniently not notice because it's easier that way.
Be very carefull with things like these The next time you might not be that luck This time you made money what if next time you ;loose and it show up on their radar system that you are using margin on which you are not allowed it is preety dangerous stuff. You could blow your account like that