I understand why you're feeling frustrated. It's always disappointing to make silly mistakes, especially in a subject that you're passionate about.
It sounds like you're a hard worker and you're clearly capable of achieving great things. The fact that you got an A* in History overall is a testament to your skills and knowledge.
One thing that might help is to try to identify the specific reasons why you made the mistakes in your History paper 2. Were you feeling stressed or anxious? Did you not have enough time to complete the questions? Did you misunderstand the instructions? Once you know the reasons for your mistakes, you can start to develop strategies to avoid them in the future.
For example, if you were feeling stressed or anxious, you could try some relaxation techniques before your exams. If you didn't have enough time to complete the questions, you could practice time management skills. And if you misunderstood the instructions, you could make sure to read them carefully and ask for clarification if you're not sure what they mean and if you want to discuss it with me so you can!
It's also important to remember that everyone makes mistakes, even the best students. The important thing is to learn from your mistakes and not let them discourage you. Keep working hard and I'm sure you'll achieve your goals.
As for your GCSE grade, I know it's disappointing that your teacher's predicted grade wasn't awarded. However, it's important to remember that the exam board's decision is based on a much larger sample of your work. It's possible that you had a bad day on the day of your exam, or that the questions were particularly challenging.
Don't let this one setback discourage you from pursuing a degree in History. If you're passionate about the subject and you're willing to work hard, I'm sure you'll be successful.