In almost every job I've every checked there has been some gap like yours around corners. How big is the actual gap at the center of the knife? If everything is smooth and gradual you may be okay. Perhaps try using a sandable primer on the wall then hold a spotlight at various angles to see if it casts an objectionable shadow. Don't use regular paint or primer (unless it is sandable) because it won't sand down and you need to be able to sand after applying more mud.
Last edited by jdougn; 03-07-2009 at 08:04 AM.