First of all, you feel insecure inside, so you need to pretend. But have you ever thought that there is no windtight wall in the world, and one day your friends and classmates will know about it, so how can they miss you? Then you say that you are going to eat or something, and they will suspect that you are not as rich in education and temperament as they are, so I think you should be honest with each other, because if you don't make friends honestly, others will.