Don't freak out too much about your marks - some of the best teachers are the hardest markers because they are pushing you for the exam. Yes, you might be doing worse than those high-scoring people... or you might even be doing better.
Rather than stressing, find some work samples from other schools to compare yourself against (for example, samples posted on this site). See if you can get some exams from companies like CPAP and NEAP, then make sure you are as good as or better than the sample answers every time. Download the Assessor's Reports from previous years and make sure your answers are at least as accurate and detailed as the samples they include.
Theoretically every person in your class could get a 50. In reality it's never going to happen, but it's all a combination of 'scaling' and the exam.