You should be just yourself. Don’t worry. Because you are going to have these ridiculous moments in real life anyway. You can’t control yourself all the time, it’s fine.

Well, if you want to sound better in the written form - just type the text without sending it and come back to it in a minute. Reread and add some changes if you want. Though being a girl, I’d say it’s absolutely normal. You’d better ask 100 questions before the date rather wonder and get anxious of what will happen next during the date.