Go with the choices you feel happy with now, Laura. Schools and colleges have an unfortunate tendency to give you to understand that GCSEs etc are something you only ever get one chance at. This is not true and you can keep picking up qualifications if you want to - you might have to pay towards them as you get older but you can nonetheless always choose to take up a new GCSE or A-level. In addition, studying for A-levels is very different to GCSE and there is always the chance that you won't take to it and drop out. So do what you enjoy now and make later decisions, later.