That's good! I take triple science and our teacher said the national average for the recent mocks was 20%. I'd say don't doubt the subjects you think will be easier, I took history last year and was getting A*'s all year but ended with an A. But French, I got B/C's all year but ended up with an A. Make time for all your subjects. Mocks are designed to make us stress so we actually work. I wouldn't worry too much as long as your revising. Some previous Y11's have told me they were getting 4's but most ended up with 7/8's. Your grades are meant to increase by a least 2 grades is what I got told.