Does PGCE really prepare you to be a teacher?

I'm at the end of my PGCE at the moment and I should (fingers crossed) pass my professional practice (being in a school). However, every now and again I am teaching awful lessons (this happens maybe 1 in every 10 lessons). Lessons where I struggle to think of a single good thing that happened. Lessons where I feel like I don't show half of what I can do. Is this normal? I feel like I let my mentor and my school down any time I don't teach to a certain standard but then they can't expect perfection from every lesson right?

What I'm hoping someone will tell me is that this is all part of learning and with teaching you never stop learning because I am freaking out that a couple bad lessons if going to cost me my PGCE. It's just right now I'm being looked at for every move I make and it's making me doubt if I can even do this but in real life teaching not every lesson is perfect right?