Relax, IELTS Is A Test Of English Only
No matter your level in English language, you must be clear what IELTS is not. IELTS is not a test of your general knowledge, IQ or even your personality.
So, speak freely, admit your ignorance about topics without hesitation, and have fun! You are going there just to interact in English.
In the same spirit, the topic you are asked to speak upon (cue-card), the questions you are asked etc, are familiar ones, and do not require any specialised knowledge.
- ignorance: lack of knowledge, information, or education
- hesitate: to be slow to act, speak, or decide; to pause in uncertainty; waver
- specialised: applying to or characterized by or distinguishing something particular or special or unique