Elias here with Shopify Support. Thank you for reaching out!
It sounds like you're trying to reach the checkout from the Storefront editor. Not to worry, there isn't anything wrong with your checkout.
The Storefront editor is for designing your store and isn't able to navigate outside of your store, which includes the checkout. Though you can edit certain elements of your checkout in the Theme settings, the checkout is a secured area of Shopify and isn't part of the Storefront editor. If you're looking to test your checkout or payment gateway, you'll want to visit your store by opening a separate window using the direct URL. Alternatively, you can also use the preview functions within your admin - Which looks like this:
I hope this helps! If you have any other questions on this topic, don't hesitate to let me know!