There's a boy in my maths class who is insanely good at maths. His natural mathematic ability is through the roof and the way he talks about maths, you can see his passion.
Thing is, he still makes mistakes. He didn't get an A* at A level maths (which we did in Y12) because he didn't do that great in exams. Everyone is going to and you can't be perfect all the time. You can get so engrossed in what you are doing and be so engaged with the complicated methods that you are going to make stupid mistakes.
If you think you are passionate about maths, study it in the future. I love maths but I don't really enjoy all the theoretical pure maths, I prefer it with an application and a purpose. There are lots of degrees out there that are highly mathematical without being a straight maths degree!