It’s a big risk only doing 3 as it limits you massively. Poetry is awful and so boring to revise but you could be asked a question on :
Power of humans
Power of nature
Effects of conflict
Reality of conflict
Loss and absence
Memory
Identity
So if you are looking to get at least a pass I advice you look over each poem and maybe write about the context behind it , the themes which ar explored in it and then a few quotes. Can’t stess enough how important it is that you know a little about each. Obviously we are very limited on time so I recommend you do
My last duchess, ozymandias , storm on the island , remains, bayonet charge , exposure , poppies, London , war photographer
Doing just 3 will make you panic in the exam as it’s possible those 3 will not pop up and if they do you may not know another poem to compare it with.
Best of luck !!