shield not working

So I was mining and I saw 2 creepers 1 exploded and hit the other and so I hit the creeper 2 times and so I put my shield up after I hit it the second time and when I did the creeper exploded 1.2 seconds later than boom I'm dead and this is in hardcore which I spent 8 hours on so I got made I was live-streaming the thing rewatched it and the shield it did not work.