Don't worry about it. My lesson yesterday, the one before my test was horrible too. I told my instructor that was me getting all my mistakes out of the way so I didn't make any in the test! Messing up made me switch on that much more when it came to the test; when my instructor picked me up I drove almost perfectly to the test centre. Other than the nerves, you are always a little more on the ball in tests anyway. And there's also the fact that you have good and bad days, as long as you don't let it get you down, you'll benefit from it.
And don't worry too much about stalling either. I stalled twice on my test today and didn't get a minor for either of them, just remember to secure the car and get it going as soon as you are able.
(Let's not mention the fact that I failed this morning! Other than the one place I messed up, as I always do on that junction, I drove better than I usually do because it was my test and that's what I had to do).