The oral work you do for GCSE builds on all you have done in earlier years.
You will be able to remember that only a few students actually enjoyed it and most of them found it very difficult.
Many students didn't take it seriously anyway and did not prepare their work.
Just because you stammer doesn't mean that you need to worry more than the rest of them.
If you work hard on the content of what you say, and practice good communication methods, you will probably be better prepared than the rest are.
Give yourself a head start over the rest. Start to prepare early in Year 10.