Hi @ErickaMurchison ,
Thanks for reaching out. Even though the myshopify.com URL you started with cannot be changed, you can add your own domain to the store and make this your primary domain, meaning this is what customers will see when you browse the online store. This should effectively mask the myshopify.com URL of your store from view and your custom domain will be the public URL used instead.
In terms of the POS you should not have any issues, as the URLs on your store are used to access the online store and are not really applicable to the POS. You can check and ensure that your store name is correct in Settings > General, as this is what may appear on some POS functions (e.g. receipts).
I hope this explains things for you, but please let me know if you have further questions.
Kind regards,
Victor | Shopify Social Care