Just to test what I have learned so far. Better to have a 100 amp main in a panel rated 200 amp, then the other way around. Though it is common to have 20 slots on that hundred , the only way to know for sure would be to do a load calculation. Red flag may be raised , but if you are not sure a regular electrician should check it out. As we all know the totals of breaker amp ratings regularly exceed the main breaker , due to the fact they are not all being used at the same time. Now I step back for my chew down.