I do agree with you that your English is good. But the speaking section in the TOEFL does not really measure your English fluency. I am not sure how long did you practice for the exam and also I don't know how did you practice for it, but I think you need to practice on the speaking prompts that can come in the real exam. Also you need to time yourself. I think the most effective strategy is to think fast and speak slow.
Anyway, good luck in your next exam.