Yeah learning can never go to waste. All my studying for JMSS, is helping with my science and maths at school, it seems pretty easy. A
Don't worry about having bad grades as most people that have done the test must have bad grades for atleast some of the tests (they wouldn't have had time to focus on school tests). For example, I got like 3 Ds for my term 2 tests (thankfully none were maths or science-related).
I got grade A at maths and C for science, however, I always get more than 85% on science tests, and 90% for mathematics tests (also, I failed English) . Plus, i’m regarded as a science guy at school (even they don’t check that) .
But the results are not yet known, on the optimistic side we might get in, and on the pessimistic side we might fail at the same time. Expect the best, prepare for disaster (KSP teach me that).