Hmmm, I'm not sure how to help. I can't throw small balls (tennis balls, baseballs, softballs, even apples on our farm!) but I can throw large balls like basketballs or soccer balls. It sounds like your ball is larger than the ones I have issues with! Oh, and I can throw a nice spiral football pass, too. Luckily, my quarterback father taught me that when I was so young that it took (apparently).
Have you tried throwing it with two hands? Are you doing it over hand or under hand? Or even side-arm? Sometimes an unorthodox position helps!