Exam Help!

On Tuesday I had my very first college exam for my Astronomy class. I was so certain that I was going to get an A on the test. I had prepared myself for the test and studied for hours with my study group. We studied for about six hours all together. I made myself flashcards and we all helped each other understand the concepts and ideas that were going to be on the test. I also studied for about an hour before going into the testing Lab. I walked into the testing lab feeling confident because I had studied many days and put forth a lot of effort. Getting good grades are important to me, so I tried my best to study. I have always been a bad test taker and even when I am prepared I get nervous and blank out. On Tuesday my mind was open and I told myself I wasn’t going to blank out because I had prepared myself for the exam. Once I was done with the exam, I went through the test again but then I doubled guessed myself and thought, oh maybe it’s this answer instead. Then I changed some answers and hoped for the best. I turned in the scan tron to the girl so she could run it through the machine. They give me the score back right away by looking at the computer screen. When I saw my grade, I was in shock. I got a 74%, even though some people may not think that’s a bad grade I did because I was so positive my grade wouldn’t be less than a B. I was disappointed and upset because I spent so many hours studying. How can I become better at taking tests? Is studying for many hours not good enough for getting a decent grade? Are there tips for being a better test taker? I really want to succeed in college and grades are important to me.