If it makes you feel better I did terribly too. And like you I also psyched myself out.
I had to re-learn Physics in 3 months time for this Test!
I know sour grapes and all but come on...my head was literally spinning while giving this test. It is so much against time that unless you have worked out lots ( and lots ..and lots ) of problems and mugged all the formulas can you hope to get a good score. I did not think I did so poorly but what the heck. And I don't think it is an indication of intellectual ability in Physics because of the super speed expected. While preparing I solved nearly every sum I ran across at my home through reasoning and understanding so I am convinced I am good.
Dont get disheartened. You have a clear passion which is rare. Keep it going. Nothing is going to stop me from trying to get into a Ph.d program in Physics. Neither should you!