I have a really small head too. I have two different helmets, both fit me well and are small size. But they both still looked like gigantic mushrooms on my head when I was a new rider, and I felt weird wearing them. But now I have gotten used to how they look and they just don't seem that out of proportion to me anymore.
It's become a less important issue to me over time, they just don't seem so oversized to me anymore.