I assume that you're trying to log into your Gmail account via your web browser, Emmie, rather than with a dedicated email client (such as the Windows 10 Mail app or Thunderbird).
If so, try clearing your browser's cache. (If you need instructions, please tell us which browser you're using).
If you're actually using an email app, rather than a web browser, simply delete the account and then create it again. (You won't lose any existing mail).