Elias here with Shopify Support. Thank you for reaching out.
Our Support team can absolutely help with changing the currency for your store and this will only take a few minutes. However, as we're unable to provide account-specific support via Community Forums, we'd be happy to assist you with changing your store currency through live chat, email, or callback. Please visit Shopify Help Center and log into your account to create a support request. Once you've logged into your account, simply complete a search (eg. Change currency) and select Contact Support at the bottom of the search results.
As you've already made your first sale, please be aware that changing the currency affects the following aspects in your store:
With Shopify actively encouraging merchants in some instances to adjust currency for new features, we want to make sure merchants are properly aware of any potential areas they need to be aware of for their account. That being said, there are also some possible workarounds!
I hope this points you in the right direction! If you have any other questions on this topic, please don't hesitate to let me know!