You do realize there is a bias here right?
Try going through your tests and also determining how many you got RIGHT when you guessed 50/50.
Generally its not gonna be an exact 50-50 guess either. Usually you will have some reason to think one answer is SLIGHTLY better or worse, making it 55:45 or something like that. Its better to choose the one you think is most right, but the one you assign a 45% chance of being right, will be the right answer some % of the time. This isnt a big deal when you are literally torn between two answer choices, but often you eliminate two choices, and then choose the best answer between 2 choices. When you get the answer right, you attribute it to your knowledge of knowing that the right answer was the best answer, but when you get it wrong, most people have a tendency to look at it as choosing the wrong choice out of the 2 remaining.
There is no real point of what i said, but stresses the importance of being honest with yourself in order to obtain the best improvement as well as the importance of reviewing wrong and right answers.
Of course you can also be correct in saying you are missing a lot more 50/50 questions than expected. This could be a sign that you are good at eliminating wrong answers, but highly susceptible to the ear pleasing trap answers.
(this reminds me of a mcat type question "Assuming the following are true, which statement best explains X according to the passage?")