First thing - don't compare your score to others on this site! Each person has his or her own capabilities and expectations.
I know how you feel. I was expecting at least a 550+ but got a 480 (Q27, V28) on my first attempt last week. My practice tests were all in the 600+ range. I've taken this week off to clear my head and get motivated again so I started back up this weekend. I've been more active on this board and I think it has helped. Everyone here has a great attitude and offer great advice.
My advice to you is take some time off and clear your mind. Then come back with a furious vengeance to conquer the test! The time off really helped me! Keep an error log
and go to town! Start with the basics and go from there.
Hang in there and don't give up! People generally say to plan for 2-3 attempts before you get the score you want so if you think about it, we just took a "warm up" test