You have to take a step back and think, do I want to do another year? What difference will another year make? If I tried really hard and dedicated all my time to my studies, would I achieve higher grades? Is this the apex of my potential for a levels? Ect.
I redid a year and I don't regret it. It's not something I wanted to do but I had changes in my personal life and my health deteriorated which made college more difficult.
It's something you need to discuss with your school/college, they might not allow it or want you to take the AS paper. If you're planning on sitting the exams this year, you need to enquire immediately if [retaking a year] would be an option for you.
There are other options though- like someone has said you, could take a foundation year.