is bellows breath only repeatable once?

Yes — Bellows Breath can only be repeated once.

It has a single Repeat cost ([Repeat] [1][C]), and each instance of Repeat can only be paid once per spell (Rule 820.1.c.3). Paying it makes the spell resolve twice total — you get your normal effect plus one extra execution with new choices (new location and units allowed). For a spell to go off more than twice you'd need multiple instances of Repeat (e.g., printed plus granted by another effect, Rule 820.3), and Bellows Breath only has one.