For shorter essays, I tend to go for more depth than breadth, though it really depends on what content you have studied so far. Base your essay off your studies so far and try to demonstrate the knowledge you have.
Evidence can include viewpoints/ quotes from academic journals (just make sure the source is trust worthy), you could include legislation or case law if it supports/ is relevant to your argument. There is usually no set way of adding evidence: ‘this is evident in case X, where the judgement is X’, as long as the essay and paragraphs flow I do not think it is too much of a problem.
Whilst it does not count towards the grade, I understand that you can be stressed about it. It is normal to feel this way, try your best to complete the essay (ensure you answer the question that is actually being asked), and you should do fine. This essay can be seen as a stepping stone, it allows you to reflect on what you have learn so far, and you will be able to build on any feedback that you receive.
Hope this helps.
-University of Kent Student Rep