Chill please. GCSEs are not a death sentance, neither are A Levels.
A Levels aren't even that bad as people say they are. People say they're hard because they employ the poor revision strategies they used at GCSE; GCSEs are quite frankly a joke and are used mainly for stats for high schools.
If you actually sit down and try to appreciate the subject content when studying your A Levels, it's a lot easier and it helps if you revise constantly and consistently.
Why are you panicking so much about GCSEs? Honestly, they're bullsh**.