That is exactly how I was last year. Same grade requirements, same thing with friends all having lower offers, same thoughts running through my head. And I'm sure so many other people are feeling it, even if they're not people you are friends with. But the truth is, I met my offer and so will most other people feeling like you. You have to detach yourself from this and enjoy the summer.
Right now make an action plan for if you do mess up: unlikely, but it does happen and really isn't the end of the world. You can retake your A levels or if you miss it by a grade get a remark/reapply next year. Maybe plan a gap year you could do. Whatever you want, just do a step by step. Also get the numbers of the admissions tutors of your first choice and insurance, and any other courses you might want to do that are available in clearing (in the papers the day before so leave that until the very last minute).
Then (and this bit is very important) put all your lists and numbers and so on in a box, keep it somewhere safe and try to put it to the very back of your mind until the night before results. You've done all you can after that. Plan a holiday with friends, throw yourself into a full time job, go out lots, anything and everything to take your mind off it. You have a really long summer to enjoy and either way with the results, you have a plan and you'll be fine!