US visa is the fairest you can possibly ever imagine. US does your background check and take security clearances from its embassies around the world on you before you appear for an interview, that's how strong their resources are. Even when you book a trip they take security clearances again on you before you board the plane, if not cleared they won't let you board the plane. If your visa is rejected, you can apply again and another visa officer might give you one. My advice is, no matter how nervous you are (its natural to be nervous and its perfectly okay), no matter if you are able to properly answer a question or not but NEVER EVER lie to a visa officer, whatever it is, tell the truth and you will be fine. Don't try to be creative and make up stories. That's it. If rejected you can always apply again but if you lied then that's on record and they share record with other countries as well I think. In fact, that's for every country you apply for, never lie on your visa application.