You don't need to worry. As long as you have a C in maths and english language and have a C in the subjects you want to take at alevel you will be fine (Some subjects may ask for a higher grade though. For example I needed a B in Chemistry and a B in maths to take A-Level chemistry). An employer in the future isn't going to choose one person over another just because they have higher grades in their GCSES. A-Levels are much more important and even then if you do go to university, your degree is a lot more important than your a-levels.