As the U.S. Immigration procedure can be extremely complex, and the process of being approved for entry in the U.S. can be very stressful, it is only natural to feel that once you are approved, and your feet are on U.S. soil, that the battle is over.
However, it is important to remember that you are not out of the woods yet. In many ways, you will never be out of the woods. Without a doubt, the toughest part of the process is behind you, but you must be vigilant and make sure that any time your immigration status comes into question, that there are never any mistakes.
One way that people can find themselves in trouble is right after entering the U.S. They may find themselves face-to-face with an immigration officer who is saying that something is wrong with their visa. Everyone is human, and everyone makes mistakes, so if this should ever happen, do not panic. Not every immigration officer will be trained on every different type of visa. It is important that, before anything, you review all your immigration paperwork to make sure there are absolutely no mistakes (visa type, admission date, etc.).
If an immigration officer does stop you for a mistake they see on your paperwork, make sure you request to speak with a supervisor to get it sorted out. If the situation is still not resolved after that point, make sure that you write down as much information as possible, such as where the incident happened, names/badge numbers of the officer(s) involved, specific problems they mentioned, etc.
Make sure you keep that information close at hand, and get in touch with an experienced immigration attorney immediately. The sooner the issues can be worked out, the sooner you can be on your way, and things can get back to normal.