In this context, "outrageous fortune" refers to the way that fate has dealt Hamlet a cruel hand. He has lost his father, and now his mother has remarried his uncle. Hamlet feels like he has been dealt an unfair blow by fortune, and he is struggling to come to terms with this.
The phrase "outrageous fortune" also reflects Hamlet's view of the world as a place of chaos and uncertainty. He feels like he has no control over his life, and he is at the mercy of fate. This sense of powerlessness is one of the things that drives Hamlet to madness.
Ultimately, the phrase "outrageous fortune" is a reflection of Hamlet's state of mind. He is a deeply troubled young man who is struggling to cope with the challenges that life has thrown his way.