I've never seen a Specialized helmet that didn't look way too big on the user's head. I'm not sure if that's because they look huge, or if it's because everyone wearing them wears a size larger than they should. It's like the older guys that wear size 13 New Balances when they are obviously a 10.5.
If you don't like the way the Prevail II feels, return it and get something else. There are literally hundreds of helmets on the market. No reason to trap yourself into something you don't care for.