If your site is with Bluehost, they should be able to give you the DNS settings needed to point the main domain to your Bluehost website (the settings will be specific to their server). Once you've got that set up and confirmed to be working, you can approach the ConvertKit setup again. Based on what you're describing it sounds like you set up the entire domain to point to ConvertKit.
Take a look at these instructions113, specifically ensuring that you set up a subdomain and include the appropriate "Host" value when doing son. This is likely where the error occurred.
Don't feel bad... changing DNS is not simple at all, it's one of the most common places where folks make errors when configuring their websites. I've goofed up DNS several times in my 20+ years of working on the web. The good news is that it can be fixed.