For your own benefit you should attend every class you possibly can, but missing a class is not the end of the world. Some beginning students feel that if they miss a class, that is it. They think they have missed so much material they will never catch up. At the very least they are now psychologically primed to slack off in interest or enthusiasm.
I encourage you to fight that tendency, for more than one reason. The first reason is that you are attacking your own psyche with an excuse designed to give you an out. The second reason is that classes are necessarily repetitive, because the material is so deep that it takes a while for it to sink in, and there is no limit to the levels of understanding you can achieve. The only barrier is your own mind. My goal as teacher is to help you unshackle your self-imposed bounds. A lesson is like a drill that goes a little deeper with each use. A drill with unlimited depth!