I'm Ann, from the team here at Shopify :)
It's hard to see what you mean without an example or screenshot, but what I think might be happening is you tested your store in another theme, and haven't ended that preview yet. If that's the case, this is what you should be seeing in your store:
So this means that you clicked to 'preview' one of the other themes saved in your account, what that does is it will show you what your store looks like in another theme, without you fully committing to it. If you click the button to cancel the theme preview, that will remove the preview and you will see your online store go back to its original state. It's also good to know that your customers won't see this preview, it's something only you can see on your end. If you like the way your store looks with this preview, you can publish the theme you are seeing by following the steps on this page in our Shopify Manual.
I hope this helps! If you're still having trouble with this, or you were referring to something else, feel free to reach out to our support team directly here - we can definitely help you out with this :)
Have a great one,
Same! I'd really love an answer as to how to remove this black bar from the bottom of my site page every time I refresh. I know how to use the Shopify dashboard without having to navigate to it from my website, and I'd love to not have to hit this X to remove it constantly. Any help would be super appreciated!