I am also weak in observing which part of diagram that i should compare and noted in the essay.
Don't sweat the small stuff, dear. Overall, your job is already good :D
Good luck for your exam.
uupppsss, a good note I found on net below:
Single graphsIntroduction: Here you sould state what the graph shows
Short body paragraph: state the most important piece of information here (summary/overview)
Main body paragraphs: Here you need to make comparisons and state the important features of the graphs (usually 2 paragraphs)
Double graphsIntroduction: Write one sentence, but introduce each chart separately e.g "This first bart chart shows..., and the second chart illustrates
Short body: Write 2 sentences. If the information in the charts is not connected, find one main point or general trend for each chart. If the charts are connected, try to make comparisons
Main body paragraphs: If the two charts are completely different (e.g. a graph and a table), write a separate paragraph about each. If the charts are the same, and show the same information (e.g. 2 pie charts), do not describe them separately, the examiner will want to see comparisons. In this case, you could write one paragraph describing all of the information, but it is still more preferable to write two paragraphs because it makes the essay look more organized