Trust me, GCSE's are easy. Ive got biology AS Level on wednesday and they are easily 20x harder.
For the GCSE if you need any specific help then ask me if you want, be confident in uour awnsers and use the key terms. If you ar erunning oht of time and yo have a few questions left dont be afraid to bullet point. If you havent already to times past papers and then mark it yourself afterwards.