yes definitely you are capable enough your gcse results are really good!! sociology is fine but an a-level subject like maths might be more useful and may make your application to university more competitive (physics alternatively would make your application more competitive), if you're applying to a top uni like imperial. but at the end of the day, you should do the subjects that you think you're going to do best at and that you genuinely like, so if sociology best fits that description, then go with that