Did you confirm the queue at the end? When you nearly reached the end of the queue, you should receive a notification to confirm that you are still there and want to start your server. Click on the notification or on the button on the "Server" page (https://aternos.org/server/) to confirm and start your server.
The Aternos forums are now deprecated
Learn more about this change here.
For help regarding Aternos, we recommend you to visit our support center.