If you want to change what it says on the 'Join us' button, e.g. 'Register here' or any other alternative, you will need to make sure the right registration link is added manually. (Only the words 'Join Us' are automatically recognised as needing to link to your Event Organiser's registration link.)

Click on the button to edit the label, and then manually change the link to match your unique registration link displayed on your Manage page Settings tab. make sure you press Save.