If you believe in free will, and you’re right — well, then you’re right. That’s a good thing.
But if you believe in free will, and you’re wrong — well, that means you were fated to have incorrect beliefs, and there’s nothing you could possibly have done to change that. It would be meaningless to say that you “ought to” believe differently.
So if you believe in free will, don’t worry about the possibility of being wrong. If you were wrong, there wouldn’t be anything you could do about it anyway.