This is likely the result of custom coding (CSS/javascript) in the pagewrapper assigned to your TeamRaiser event.  The formatting will have to be adjusted if it is hiding a portion of the participant center.  Since custom content is not supported, please reach out to your web designer to have them address this issue by following the steps below:

  1.  Make sure the Participant Center is up to date. You can use the following help document to accomplish this:
  2. Add the following custom CSS code to the Participant Center "Edit Custom Styles" page:

    iframe.seamless {
    border-radius: 5px !important;
    width: 1200px !important;

Instructions on editing the Custom Styles sheet can be found here: custom style
Please note that CSS knowledge is required to make these changes.