Oh no! Now what??
As I can see you already own zoom lenses which cover the mid focal lengths. If I were you I would buy the prime one in no time. It is sharper and the AF system also faster. I would recommend the 100-400mm ONLY to those who want only one lens to cover the whole focal length range.
Here is a sample of my 400mm f/5.6 L "African experience".
You can check out sharpness and fast focus ability in action shots by yourself! Greetings from Greece