Seriously, if you've taken our advice and worked hard enough to get the grades your teachers predicted, you should be OK tomorrow, into your first choice or at worst a decent insurance.
If you've got serious concerns that something went badly wrong in the exams, then do some preparation NOW!
1. Check the phone numbers of the Admissions Tutors of your Firm and Insurance choices. Near misses are often allowed in anyway, but be prepared to get on the phone and schmooze - persuade them that you totally love their university, and that is was just because your guinea-pig died on the morning of the C4 exam that you slipped a bit.
2. If you are REALLY worried, get familiar with the Clearing Process now: http://www.ucas.com/clearing
Watch the video a couple of times, and do a preliminary search for courses you might be able to get on if all else fails.
3. If your results are not what you hoped for, and you can't find anything suitable in Clearing, there's always the option of a 'forced' gap year. You can always pretend you were planning one all along. Get a job, get some experience, learn a language, do something for other people, and reapply from a position of strength (you know your results) and maturity. Get some help - get in touch.