Delivery

I had my first observed the lesson the other day, and I am noticing a trend. The more I prepare, and the better my lesson plans are, the worse my delivery is, and the less I am able to stick to the plan. I prepared a really thorough lesson for my first observation of the year, and when my teacher came to observe, I found myself more nervous than I usually am when I "wing it" and kind of unsure. The students had studied, were extra respectful and attentive, and did a wonderful job of showing how "on the ball" they were. I have never been prouder of a group of students I have taught. Unlike the last time I had a lesson I felt like I flubbed, this time it was not the students. (Last time they were just not on the same page as me. This time, if they weren't, they jumped to my page-- they were ever eager to keep up with me.) I over-planned the lesson and ended up having to cut out a few things, and forgot a few things in my harried state.

What I want to understand is, why, when I am so prepared and have such a clear idea of how things will go, do things always go much less smoothly than when I just plan an idea of what I will do so that I can see where the kids take it? I want to prepare good, strong lesson plans and deliver them effectively in the classroom. Is this counter-productive to my teaching style?