Got a photo? I’m just wondering how bad it is. Try the tap if you have one, a thread chaser kit is a good investment. https://www.amazon.com/Lang-972-Fractional-Metric-Restorer/dp/B000P6UNHE/ref=sr_1_5?crid=AQS47RTTLQHY&keywords=thread+chaser+kit&qid=1564946899&s=gateway&sprefix=thread+chaser%2Caps%2C182&sr=8-5
Maybe you used 1/8-27 NPT (national pipe thread) plug? Also, a 1/8-28 BSPT (british standard pipe thread taper) is available.