Firstly, A-levels are far more important than GCSE's, if you really want a place, you need to aim high and work really hard. Universities would be fools, if they regarded a B at GCSE far more important than an A at A-level. Remember there is a big jump between GCSE's and A-Levels. If you are willing to do high-demanding courses which require AAA, you need to plan your time and what you are doing now is great, but I would highly recommend if you do go over (even if you skim read the topics you are going to do the upcoming lesson), because then you would know at least 10% of the information. Work experience enhances your personal statement. Apparently, there is one in the October half-term in London so go check that out.