Electrical Question about a 100 amp sub-panel to a 100 amp sub panel in my out-building
I'm with Kris. A 100A breakers lugs are sized for a #4 through a 1/0 which is one size larger than the required #1 aluminum. I guess what you are saying is that you have run an over sized feeder. 

Since you have already run the feeder you might need to reduce the conductor to fit the breaker lugs using an insulated butt splice, like the picture, inside the panel.



Good Luck