Rae from Shopify here. Thanks for posting this question, and welcome to the Shopify Community!
When did you first open your Shopify account? Do you recall if you signed up for a 90-day free trial via this link?
If you haven't selected a pricing plan for your store yet, the amount of time left on your trial will display on a banner on the 'Home' section of your Shopify admin on the bottom of the page.
Though, if you have selected a plan already, then I recommend looking in the 'Settings > Billing' section of your admin to find out when your next bill is, and to see upcoming charges. When looking in this section, if you don't see a subscription charge on your upcoming bill, that means that you're still on a free trial with us.
When choosing a plan before your trial ends, you won't be charged for this plan until your trial time has finished, as outlined here. However, if you've downloaded any apps, purchased a theme or a domain, or made any sales that incurred transaction fees or credit card fees, these items will be billed to you regardless of whether you're on a trial, or a subscription plan, with us. You can read more details on this here.
I hope this helps! If you have any other questions or concerns about your trial time, or our billing, please let me know.
In the meantime, I'd love to hear a bit more about the business you're building. Do you need any help deciding which pricing plan will work best for you? Or, have you already launched your store? If you need any assistance with this, or if you'd like to discuss your business further, I'm glad to help!