Honestly, I felt the same way as you seeing my AS results, and I thought I would do better! Just stay positive and remember that this doesn't define you. I'm sure you are a really intelligent and capable person, hence why you are so upset. I would consider resitting year 12 as sooooo many uni's don't dislike resitters. For example, Loughborough are pretty chill when it comes to that. If you resit more university options will be open to you than if you chose not to, and you can spend an extra year building about your PS even more with new extra-curricular activities.
I hope this helps, and don't feel bad. I, and sooo many other people, are in the same position as you.