I have a job for 6 mths. I was supposed to get a raise at 3 mths, Now my boss says I am not detail oriented. ?

How do I become detail oriented and what should I do about the pay. I have 2 kids and I am a full time college student. I have really great insurance and the people I work with are good,down to earth, and very kind. I am in college for CAD so I really need to be detail oriented ( I thought I was).