[Alumiyum]

As everyone has said, you need to go. Plans with friends, parties, etc. are not reasons to miss chapter at all, especially when it's your first one as well as your pledging ceremony. Unless it is an excuse that would be valid for class or work (legal obligations, serious illness, family emergencies or funerals, or university obligations), you need to go. Your plans can be rearranged. This is not the first time you'll have to make this choice by any means, and it's a good lesson in priorities, because in the real world you'll hold down a job and you'll need to show up unless you have a damn good reason not to.