Normally first 10 questions are crucial and you may get all 3 types of questions in the first 10 questions. There is no predefined sequence of the questions to appear.
It will be better if you try to strengthen your weak area instead of panicking. Grasp the strategies for each category and practice with individual questions and CATs. While practicing, analyze each of your answers irrespective of accuracy. Additionally, if RC is the weak area, read lot of good articles. If SC is the weak area, refresh your grammar. GMAT is a mix of sprint and marathon - you need speed and, most importantly, you need to stay calm at the same time.
Hopefully this will help you. All the best.