I took a couple hits of a joint about 3 1/2 months ago. I had a hair test yesterday and they used chest hair... will that small usage show up

Doubt it.

A hair drug test is meant to show consistent use over time. Body hair has a long growth cycle so any body hair test will give about a 12 month history of use. But with the small amount you did I doubt even if the limits of detection (LOD) hair drug test would be positive. I wouldn't worry if I were you.