Well, you could have saved yourself some money (and not had this problem) by using a main lug panel since a main breaker is not required in this sub panel. You have a 100A feeder that is protected by a 100A breaker.
That said, I can't see any code article that this would violate. You could say that it is simply a disconnect which are often sized larger than their circuit OCPD.
-Hal
