The overthinking part on whether or not your speech is perfect may stem from your observations on other people being perfect at a single given moment or a very few moments; or maybe if you consume too much movies/TV where their delivery is perfect 10/10 and you want what they got after delivering perfect lines/speech.

It’s good that you’re aware that it’s all a flaw in your thoughts, next thing you should be figuring out is why do these thoughts come in the first place? What would you achieve by being a perfect speaker? You maybe be overthinking this perfect speech part because you want something by appearing a perfect speaker and you’re afraid of if you don’t deliver a perfect speech you’d be at a disadvantage with what you want by appearing perfect.

After realising this, understand you can’t really control how others perceive you, even if you give a 10/10 speech, there’s a great chance no one would even mildly notice how good it was and appreciate or give you whatever you wanted by delivering perfect sentences.

Insecurity comes from within, look deep within you, understand why exactly your thoughts are the way they are.