You cannot use a dictionary in the speaking exam. You cannot make any written notes in the speaking exam. Don't spend time worrying over mistakes. It will tend to interrupt the flow of your answer. However if you do realise a mistake you can easily correct yourself.
Communication is the main purpose.
There are many ways of expressing the same idea. However, if you say nothing, no communication is achieved. Make your delivery sound convincing. Use appropriate intonation, emphasis and correct pronunciation. Make sure that your responses are appropriate to the questions asked.