If your invigilator forgot to put the barcode or sticker on your english HSC boards improvement exam paper you should not panic but act quickly forst inform your school or exam centerabout the issue as soon as possible and explain the situation clearly if they are not able to help then contact the HSC board directly and report the mistake you should write the formal application or email mentioning your name roll number  subject and date of exam along with the brief explanation of what happened it's important to act now so that your answer sheet can be properly traced and evaluate