Don’t stress too much, we all make mistakes during bonding!
But definitely make sure the next session is in neutral territory! I would continue doing pre-bonding (side swaps) for another week or so. This will let them calm down a bit from the fight as well. The initial grooming was very good, the fight not so good, but not the end of the world (assuming no bun was hurt?).
In future sessions be sure to prevent fights before they happen. So be ready right there to get your hands on them as soon as they get close to each other so you can stop things before they escalate. If you find they fight right away in neutral space, then go back to a bit more pre-bonding and you might try some stress sessions.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.