General GMAT Questions and Strategies | I don't know what to do

I'm here because I don't know what to do. I've been studying for the GMAT since November. I don't have much time per day because I work 40 hours a week, but I try to put in a minimum of 10 hours a week. All of my practice test have been in the 550 - 590 range with an average of Q30 V32. But the first time I took the official test in December I got a 450 (Q21, V30). I have since taken more practice test with very little improvement. I enrolled in a prep course and took it twice (I won't name the