Your son has learned a lesson. He is not likely to talk during a test again no matter what the situation is. More importantly, he has also learned that if he breaks a test rule, there will be a penalty. It is a good lesson to learn before grades truly become important.
Few people enjoy tests, and many, like your son, panic when anything goes wrong during a test. You can teach your son techniques to avoid alignment problems in the future. Suggest that he place the test over the answer sheet so the space for the next answer is always at the top of the sheet. Also, tell him to check that his answers are aligned properly every ten questions. Some students keep their answers properly aligned with the questions by simply answering every question and never leaving a blank space. They should circle a question when they are unsure of the answer so that they can go back and change their answer if they have time.