As I understand, you are only able to watch the Slingbox in full screen. We need you to provide further information about this issue;
Are you using Watch on Slingbox.com to view the Slingbox or are you using the SlingPlayer Desktop?
Which browser are you using?
If your equipment doesn't meet the requirements, that can be the root cause of the issue. Make sure that the browser you are using is supported, use this link as a reference.
If the issue persists, make sure to provide as many details as possible. This way, other Forum users will be able to help you with accurate information.