If you want to make sure a particular world is the one you always load into, you can follow these instructions below:
- Log in and go to your dashboard here.
- Select the server you want to change and hit the Activate button to start your server.
- Once your server has started, go to the Settings tab from the top menu.
- Scroll down to go to Selected World and select your world name from the drop down, click Save Changes.
- Restart your server and you're done!
Be sure not to include any spaces or special characters in your name as it will cause issues if you need to download it.
To find out how to change a world name you already have, you can check out this article.