To be honest, it's hard, but it's not THAT hard. Yes, 60% of people get no offers, but that means 40% of people get at least one - so it's far from impossible! The better your grades, the better your chances overall, and stronger grades certainly mean you have more options open to you, but if you have reasonably decent grades and apply carefully to your strengths, then your chances are pretty reasonable. I wouldn't start work on the UKCAT just yet - save that for the summer holidays before you take it, and concentrate on your school work for now.