If you do not agree with your grade, seek the advice of your teacher, then learning leader of the course, your learning coach or administrator. It is important to note that an appeal should be in a timely fashion, within a day or two of the mark being issued.
Final exams need to be written the day they are scheduled. If you miss a diploma exam you will need to write during the next session. For school exams there are very few exceptions where students are permitted to write at a different time. This protects the integrity of the assessment. Please see an administrator to consider your options. Please note: family holidays, or early leaves, are not considered a legitimate reason for exemption.