It is a huge myth that you need 10 A*s or more at GCSE to get into oxbridge. A handful will do, honestly. 5-8 is plenty, providing you ge no low grades. Even though GCSES are important, your a levels are where most of it lies. You could get average GCSE results and still come out of a levels with A*A*A. Backed up with experience, a good application and excellent A level results, your GCSEs are not the most important thing. You will not get looked down upon for getting 8 A*s by any means, this is far higher than the national average! Do not fret!