No, chanting the Navkar Mantra three times by itself is generally not considered a pachkhan.

Pachkhan means a formal vow / renunciation / resolution taken with clear intention, usually with specific words and limits. For example: fasting, giving up a food item, or observing a restraint for a set time.

So if you only chanted:

• Navkar Mantra 3 times
• as prayer, remembrance, or devotion

then it is not usually a vow that can be “broken.”

If you had taken it as a pachkhan with intention, then breaking it means the vow was not fully maintained. In that case, Jain practice is to:

• do alochana (inner confession),
• feel repentance,
• and resolve to be more careful next time.

If you want, I can also explain the difference between Navkar Mantra jaap and pachkhan in very simple Jain terms.