It can be truly nerve wracking to go into an exam room and begin to have a spontanious conversation in a language you are not 100% familiar with, however there are methods that can help you walk in feeling more confident about your knowledge and speaking abilities. It's important to remember that you won't be asked about something that you've never learnt about before so you need to ensure you have covered all of your topics thorougly to give yourself the best chance. You can begin by going through the each topic and making up different questions and answers as well as going throught past exam papers. Next it will be time to learn the answers to your questions. One of my favourite ways to memorise long texts is by recording myself reading them and then listening to them on my way to school or just doing ramdom things, mouthing along unit I knew it off by heart. However if you're more of a visual learner you can try write out answers from memory until you get them right or write key words on post it's and put them around your room so you can be practicing without even noticing. A fun way to work on your accent and understanding is by watching Spanish films or TV shows and copying the actors with subtitles, it is actually really helpful and will definitely make a difference. Overall the key to being truly prepared is to give yourself enough time to revise and practice in whatever method or mix of methods you find helpful and to have confidence in yourself, keeping your cool and enjoy it!