CVs aren't as bad as you'd think to write. Start with your name, contact details, and address at the top left side (where the address would go in a letter). Sections to maybe include are:
personal attributes - a few key words to describe yourself (e.g. "committed, enthusiastic, engaging" etc.)
education - just put your predicted grades for now
experience - can include volunteering so anything you've done to help out in your free time, including things like school ambassadors
personal hobbies - a few things that might show you to be an all-round person (I have things like cooking, needlework, musical theatre)
references - try to get the name and number of a senior teacher (the higher up, the better so long as they personally know you) and someone external who's not a family member/friend (e.g. swim coach, scouting leader) (and obviously ask their permission first!)