It is super common, even amongst students who end up scoring A during A-Levels! There are many students that fail during Promos or Prelims even that score well in the A-Levels. It's what you do after you fail that makes the difference.
2. Don’t be discouraged over it for too long.
No need to feel demotivated or feel that it is the end of the world. A test is only a small part of your learning. Take it as a chance to reflect.
3. Reflect over your mistakes.
Take the feedback to rethink your learning based on your teachers or your friends’ advice.
4. Keep believing in yourself and work harder!
It is normal to have problems and mistakes everywhere as only through mistakes then you can learn. You would never notice certain things about the correct answers if you never got those questions wrong!