Hi there Squamber!
Don't worry too much about your grades just yet. I was in a similar situation with my AS results a couple of years ago where I was holding a B grade in English, however, I just worked even harder in Year 13 and ended up boosting that B up to an A, with no resits at A2 needed. Hopefully, your remarks, even if they stay at B grade, may go up by even a couple of UMS points which can really help, especially if you need an A for the courses you are looking at. I would not even worry or plan resitting anything just yet, speak to your teachers and see what they suggest, maybe even ring a couple of the institutions you are looking at applying to?
Whilst I do not study Law myself, my best friend does and we both attend New College of the Humanities in London. I would definitely consider you looking into NCH for Law as it is a fantastic course and the course is taught through a mixture of one-to-one tutorials, seminars and lectures. Another great thing about NCH is that whilst the university does consider your grades, NCH also asks you to attend an interview and so the university looks at more than just your grades but how you are to teach, etc.
Regardless, I would not worry too much just yet about your results. You are clearly a smart individual with the predicted grades you have at the moment and you should not be disappointed with your B, like I said, you can easily turn this into an A like I did, and even if you do not, there are plenty of doors open to you, and there are many cases of success stories where people have still got into their desired courses even if one grade is slightly lower than expected.
My advice would be to breath, relax, consider your options, look into further courses looking at universities both with high grades (A*A*A, A*AA) and some lower than AAA (it is always good to have a back-up!), speak to your teachers, and push yourself in Year 13. You can get this A in English!