The wrapper you see on a Participant Center message is set by the stationary. Stationary can be set within the TeamRaiser event or created within the Email module and assigned to use with TeamRaisers.

If your participants are seeing the wrong stationary for the event when previewing the message on the first step, this can indicate that the desired stationary has not been set as the default stationary for your event. To set the default stationary:
  1. From your TeamRaiser List click "Edit" under Actions next to the appropriate event
  2. Select Manage Stationary
  3. Choose the appropriate stationary from the drop down menu under "Default Stationery for Participant Center Email Messages:"