Remove trailing space in Mac OS hostname?

I'm trying to run Prometheus on my Mac, but I get the following

MyHostName $ prometheus --config.file=prometheus.yamlparse external URL "": parse "http://MyHostName :9090/": invalid character " " in host name

See the space between MyHostName and :?

Here's my simple prometheus.yaml file

global:  scrape_interval: 10sscrape_configs:  - job_name: prometheus    static_configs:      - targets:          - localhost:9090

How do I remove this space? I've tried the following

$ scutil --set HostName MyHostName$ scutil --set LocalHostName MyHostName$ scutil --set ComputerName MyHostName

Any clues? Thanks!