I have a science exam in the morning! I'm proper nervous about it too

- I just have this feeling that I'm gonna screw it up well bad!
Its 20% of one of the 2 Science GCSEs I'm gonna do it two years.. and it's on Chemistry (which I suck at xD) and Physics (Which I'm trying to re-cap on as we did it before the summer holidays) x
It's like my first proper exam too, like in the hall and everything.. so I don't really know what to expect! There are 2, 20 minute exams ..
Just thought I'd share it with you all! It's a teacher training day too, so all of my year have to go in at 8.45!
Anything that will help, please share xD I'm proper nervous!! Xx