Cal here from Shopify, thanks for reaching out to us. I'm sorry to hear that you are looking to close your store. Was there something, in particular, you struggled with? Is there anything we can help with?
You should be able to close the account as shown in this guide, or by following the steps below:
1. Log in to the admin section of your store.
2. Click on Settings.
3. Next, click Plans and Permissions.
4. From there, Scroll down to the bottom of the page and click "Close my Store".
Let me know if you encounter any trouble!