I understand your concern about an asteroid or comet striking Earth. This is not a subject to take lightly, but it is one that needs to be kept in perspective.
Your chances of death by asteroid are about the same as dying in a plane crash (1 in 20,000) during your lifetime. You're more liable to be electrocuted to death (1 in 5000), succumb to skin cancer, or be killed in a car crash (1in 150). Death by asteroid poses more risk than death by tornado (1 in 60,000), rattlesnake bite or food poisoning.
Worrying about such things will not decrease your odds.
A rock a hundred meters across impacting at 30 kilometers per second could wipe out an entire county.
The mathematical statistic of such an event occuring is, one such impact every few million years or so. Not enough to allow such a topic to control your daily thoughts or guide your life.
Instead of living in constant fear of the unknown, consider these facts: Planet Earth could not have accreted enough material to form into a planet without the existence of asteroids and comets. Comets contain water and carbon-based molecules. It was comet collisions with Earth 3.8 billion years ago that led to our planet having water and the necessary ingredients for life to develop and evolve. It was an impact 65 million years ago that allowed mammals to become dominant on Earth to replace dinosaur and reptilian dominance.
NASA and other organizations are doing the best they possibly can to identify and track all NEO's. Have faith and assurance in their abilities to do their jobs. If your fears and concerns persist, try joining a group such as Space Guard. Above all, avoid any websites that promote fear by presenting false information. Seek information from true science websites only.