Should drop German?Watch
If you did do GCSE German, you can still catch up by dedicating a lot of time and effort into systemtically revising and perhaps working with a good tutor. There are online resources classic printed revision guides en masse. You will need to speak with your teacher in the sense that you need advice, and if it's only someone who shows you what you've missed so far.
However, if you are generally struggling academically now at A-level, you will also need to check what you need, and if you can get the right support and environment that helps you evolve and improve in school. This can be very challenging and it's perfectly possible that you totally fail, if you don't address this consequently (speaking from own painful experience in the Gymnasium school here in Germany...)