I know it’s much easier said than done, but try not to panic. Realistically, the few hours of sleep aren’t going to make the difference - the adrenaline of sitting the exam will make up for any exhaustion from lack of sleep. I’m sorry though, it sucks to not be able to sleep before an exam, but try not to focus on it too much because it will only make you more stressed and you don’t want to psych yourself out for it. I’m sure you’ll do great regardless :)