Hi,
I understand your disappointment. But it is common at your first attempt to a full exam.
My first suggestion would be to try to understand the reason for your score: was it a time management problem? If this is the case, I'd recommend not to spend too much time on a single question until you decide which is the correct answer; sometimes it helped me to mark it and go back to that later: surprisingly, after a while I was able to get a new perspective and found the correct option much quicker.
If your performance got worse as you moved on in the exam, it may suggest you got tired and lost focus. At the beginning, I had a similar experience while practicing full exams in the afternoon: after experimenting a bit, I found the best time of the day to practice without getting too tired in the middle of the exam
I highly recommend to review all the questions: besides those answered incorrectly, I also learned a lot from those I answered correctly but were not sure about it. Try to spend more time on the areas you performed poorer, to be sure you understand the explanations provided.
Don't get discouraged: I'm sure practice will help!
Gabriella