You're "scared" because you have a warped idea of the United States. Osama bin Laden was the boogeyman for an entire generation, and now he's dead. Will this affect al-Qaeda's operational ability in the short term? No, he's just a figurehead. But that's why everyone's celebrating: the man they unequivocally associate with terror and death has been eliminated. These people are not ready to storm into Afghanistan and mow down civilians, and they're not going to hijack airliners and fly them into buildings in downtown Riyadh.
A second reason for the celebrations is that the killing of bin Laden shows that there really is no hiding from us. You can last for a while, but we WILL get you. In the face of all the America-hate the rest of the world constantly vomits every time we twitch, I know I saw this as a big "fuck you" to the rest of the world. Mocked for a decade about not being able to find "a frail old man", when it turns out that he was possibly being hid with the assistance of a so-called friendly nation. Then suddenly, 24 Navy SEALs bust down his doors and kill everyone without a single casualty, using US intelligence from US-cultivated leads. Alert Pakistan? Fuck that! He's less than a mile from their military academy! That's just a little bit suspicious!
So bear in mind that we are not celebrating the death of one man. I'm glad that his remains were handled in accordance with his beliefs. I know that the burial at sea is not a preferred method of burial for his beliefs, but it was carried out to the best of our abilities. I'm celebrating the destruction of the symbol that opposes everything I stand ready to defend. The symbol of people willing to kill me because of who I am, not what I've done. They've taken it upon themselves to be judge, jury, and executioner, and as the wrongly accused, I'm glad to see them fall.