A good way to become more fluent is having some ideas in your head about the topics you might have to talk about, as it will stop your mind going blank in the exam. Make mindmaps of the different topics you have studied this year, with key words, phrases and good, high-level vocabulary and structures, and read them over to yourself until they are in your head.
Another great way to become more fluent is listening to other people speak Spanish, watch a Spanish film on netflix (even with subtitles will help!), get into a Spanish TV series (telecinco is a personal favourite for free TV), or even watch blogs on youtube in Spanish. Find something you're into, whether it's cinema, football, beauty or celebrities, and listen to the way a native Spaniard speaks. You'll definitely pick up new phrases and a turn of phrase which will make you sound more fluent.
Before an oral exam, I try to speak as much Spanish as I can. If you're lucky, you might have a parent or classmate who you can practice with, but if not there are still a lot of ways to practice. I recite presentations to my mum - she doesn't speak a word of Spanish but it helps me feel more confident speaking in front of somebody. I even talk to myself, if you can try and get yourself in that Spanish mindframe it will help your fluency so much in the exam.