Let’s talk about mistakes. Everyone makes mistakes. Even a native English speaker makes mistakes speaking English. So they’re going to happen.
On the test don’t get too worried about it. You’re undoubtedly going to make mistakes but don’t freak out or get nervous because that’ll ruin the rest of your flow for other questions. If you can, try to correct your mistakes if you notice them immediately. But don’t say, “Oh, two sentences back I should have said this verb.” Try to correct on the spot. If you can’t just move past it and realize that they’re going to happen and it’s not that big a deal.