What tests are you using? How is your performance? Are you having plenty of time to spare after you answer the questions? Are you answering the vast majority of the questions correctly? If you are taking the ASVAB practice tests or the POSS practice and answered yes to all of the other questions with exception to "how is your performance?", you have a really good chance of passing the test.
Btw, I'm no expert. I'm not even experienced. But I have taken and passed the POSS. I firmly believe that education level will play a very small part in passing the POSS test. Experience can help with some modules. However, it's an aptitude test. Anyone with a high aptitude, a good degree of logic, reasoning ability, critical thinking, and common sense, can pass the test.
Bottom line is, you either grasp it, or you do not.