Take some breaths. It gets easier, I promise. It will still be busy, but you will get used to it. Each time you get anxious, breathe and focus on those breaths. It will help you to settle.
Firstly, your planning will be fine. I know this because you have spent time on it, which shows you are thoughtful and you are putting effort into it. You are on placement, you are there to learn - you can make mistakes and it will be fine because you will learn what you need to do differently next time.
You sound very conscientious so you must take care not to burn yourself out. If the work load feels too much, have a conversation with your mentor. You are training, you will be very, very busy - that is not unusual - but you should not start to feel overly worried, anxious or stressed. I'm a mentor and have been for many years, I always ask my trainees about how they are coping and to talk to me about their workload. I also encourage them to try and get a good block of time for themselves each weekend. You need to learn to manage the workload and it can be very full-on when doing uni essays too.
One thing to remember, perfect doesn't exist in teaching, if you try to be perfect, you will go mad!
Now, step away from the work, get your clothes sorted and make yourself a cup of tea, feet up and good telly for the rest of the evening.