I'm mad over something pretty small
I do not understand the reason for you thinking. Why has something small made you mad?
Because I knew something bad was going to happen and it did. I expected more.
You shouldn't get angry over small things. Life is too short to feel upset all of the time.
I'd rather be mad than be sad
Being mad is pretty damaging to your health and it can also damage relationships. Usually people only get angry in relationships when something bad has happened.