I like fearsomefour's advice here. Stop and take a deep breath.
You're stating that you struggle in practice sessions with your dad, what is different about those sessions? Finding out what is different that is causing those emotions and control problems may help. Is it on a different mound? Is it the environment? Is it the subconscious anxiety of disappointing your father? It could be a number of things, if you really want to find the cause, look at all of those differences.
More importantly, the deep breath is a good idea, relax, and don't try to over-correct. Just throw like you're taking your warm up tosses before an inning, as you stated you do well there.