I have never hunted elephant. But, I have shot competitively at the international level, and done well. I go through all the emotions you are going through before every large competition. Here are my two cents on how to manage these emotions.
What you are experiencing is doubt, and specifically doubt not necessarily in your ability, but also in the situation you may be faced with. This doubt can unhinge top tier competitive shooters, and hunters chasing quarry alike. In competitive shooting circles we all practice and are coached on mental management to help us shoot our best, and these practices translate directly to hunting situations.
So, here are three mental management things you can do, that will directly help you face the pressure you are putting on yourself:
1. Four square breathing. This is a relaxation technique that is proven to lower your stress levels and heart rate. If you find yourself getting amped up, fast heart rate and such, simply follow this pattern for 30-60 seconds. Breath in slowly over 4 seconds. Hold your breath for 4 seconds. Breath out slowly for 4 seconds. Hold and empty breath for 4 seconds, and repeat. If you repeat this cycle 2-4 times your body will calm down. You can do this in the last few mins before you encounter your animal, or any time you find you are stressing over the hunt.
2. Visualization. Your body tends to make happen, what your mind fixated on happening. So you need to teach your mind to see the best possible outcome. How can you do this? Well every night before you go to bed, and every morning before you get out of bed, simply lie in a comfortable position, close your eyes and remember a hunt that went well. One where you remember taking the shot, knowing the shot was great, and then walking up to the animal and seeing that the shot was great. You need to remind your brain that you are 100% capable of making great shots. Then visualize the hunt on the elephant, see it in your mind, see the elephant, imagine yourself putting the sight perfectly on the elephant, taking the perfect shot, and the elephant dropping on the spot. Imagine it from any different angles, and the shot always being perfect. What you are doing here is training your mind to take the prefect shot. Do in the morning and at night, and during any nap or anything mid day. If you train your mind to see and take the perfect shot, your body will execute your minds will when the time comes.
3. Calming thoughts. Right before you are going to be in a shooting position, imagine a calming scene. For me I imagine a wave (which I identify as stress) washing over me, but as the water leaves, I remain. I imagine the water washing away my stress, and a relaxed version of myself remaining. I practice this imagination technique right before I step onto the berm to shoot a match. It only takes 5-10 seconds and it 100% centers me before shooting.
I can tell you that mentally, these three things will help you shoot better regardless if it is at a competition or at an animal. remember that if that first shot is a good one, all the worries you have disappear.
And if you have time, I would recommend getting and reading this book: "with winning in mind - by Lanny Basham" It was written by an Olympic gold medal shooter on how he managed his mind to make perfect shoots.
The key to all of this is to make that first perfect shot. Oh... and listening to your PH!