DescentBB

I love my cowboy hat that my brother gave me. It does not fit me because its too big. I mean it fits good enough to be comfortable, but there's no way to keep it on my head while I'm outside without keeping one hand on it. It's like a sail. I've been trying to stuff it with different things to make it lock on, but it always ends up hurting. Is there a proper way of fixing this? Do I just have to go buy a new hat from the boot store?

edit:
I'm not a real cowboy.